In order to create a task
Go to "Systems (F5)"> "Intel" ; click on "create a task" and "set task state", and place them near the tasks objective. Configure your task and the task's state once it is achieved (succeeded for example).
Right click on one of the two, "connect to", and sync the two entities.
Then, go to "Triggers (F3)". Place a trigger. Then configure what the task needs to get completed (examples below). Now sync it to one of the two things from before, and you're done.
Don't forget to sync your task to the player if needed!

Synchronization order I recommand: player > create task > set task state > trigger

Examples of tasks :

- Get in vehicle: in the triggers "condition", write

- Kill a single ennemy/destroy a thing: triggers condition, write
if you want multiple things dead, like 5 men, write "!alive [name] && !alive [name]" and repeat


- Clear an area of ennemies: (not sure, have to verify soon in my scenario)
create a trigger of the desired size.
Set it to "opfor", "not present".
replace "this" by "
Videos :

• A comprehensive video on how to create a kill/destroy mission (Kill single task and destroy object)
  
  
• Really good videos to understand the basic of creating a task, with the example of picking an object and moving somewhere.
  
  
• Get in Vehicle Task
  
  
• Activating tasks in a sequence

The greatest thing to add life to your scenarios is in my opinion the animations for non-playable characters.
Doing so is pretty easy on the surface, but tends to get tougher to understand the more complex you want your animations to be.

Basically, the two simplest ways of animating characters are:
(work in progress)

• By adding the command line directly in the entity
  
  For most set of animation you can add this after the end of the command in order to stop characters idling and go back to fight when they see any hostile target
  
  _Combat
  
  
• By creating a trigger with the command inside

---

Some videos to help you

Schlimster's Arma 3 AI Animation Tutorial
To me one of the legit best tutorial to understand animations and how to get characters to go in combat mode if they see an enemy
https://www.youtube.com/watch?v=78siOse51Ng
-

Feuerex's Arma 3 Editor Tutorial - Animations (20 minutes long, a bit hard to follow imo)
Really complete tutorial, but I tend to loose the track of the video, pretty long imo
https://www.youtube.com/watch?v=nyDjbnm94n0

-

Tommy23r10's Arma 3: Animations Tutorial (3D Eden Editor) 2018
Shows a really basic way to do things you can understand, but pretty long and a lot of blabla, but I learned with it, so I thank him
https://www.youtube.com/watch?v=eQCp_-r0udU

In this section we'll see how to create different types of respawns and how to configure reanimation (for multiplayer)


In the bar at the top of your screen, go to "Attributes", "Multiplayer..".

Go for the "Respawn" section. Select the type of respawn you want (everyone of them are self explanatory, but I'll explain the "Respawn on custom position").

Respawn on Custom Position
It allows dead players to respawn on... custom positions.
It translates by a view of the map with one or several positions, and the player chooses one to respawn at.

To place a custom respawn position, go to "Systems (F5)">"Multiplayer", and place down a "Respawn Position". Double click on the placed module, and configure everything you want to.

(w o r k in progress)

1. Place an object
2. In its INIT, copy the following :

Pretty easy to do, works with triggers. You need a radio in your inventory, or it will not function (and that's completely logical).
Place down a trigger, the objects will have to pass through it to hear/receive the message.
Configure it as you want (best if you have only one side for players: Any player ; Present).

Next, you have two types of radio messages, both in "Systems (F5)">"Events". Don't forget to synchronize your message with the trigger(s).

• Radio Chat
  Sends a customized message to the unit.
  Write what you want in "Text". I recommend to put "Apply to" as "Objects in synchronized triggers". And select the channel you're message will be sent to.
  
  
• Generic Radio Message
  Sends a generic radio message and plays an audio message at the same time.
  Just select the side of the message (Blufor;Opfor;Indep;Civilian), and the message it will play.
  Beware, you need to configure a "Headquarters Entity" or the message will not play.
  Go to "Systems (F5)>"Intel" and place down "Headquarters Entity". It doesn't need to be synchronized with anything, it will just be the name displayed for one side's radio message. Really easy to configure.
  
  
• Radio message with a custom callsign
  Sends a customized message to the unit, with a customized callsign
  Simply place a trigger with the "player" and "present" (or as you need it).
  Then in the trigger activation write this function:
  
  [variable] sideChat "[message]"
  Put a variable name in the entity you want sending the message (in the attributes), and copy it in the beginning of the function (don't put the "[/]"). sideChat is the function. Then write your message between the " " (again don't put the [/]).
  
  Test it by going through your trigger.

A video to create custom messages with the names you want (instead of generic messages from HQ)


The name of the road gate (not "door" or "block", i'm a moron i never find it)
Bar gate
(yeah it's easy but I tend to forget)


Put a road gate. Give it a variable name. Put a trigger in the zone you want your vehicle / unit to be in order for the road gate to open. Set the trigger's "activation" to whatever you want ("Any player").

In "On activation" write :
In "On deactivation" write this in order to close the gate after your passage.

Solution initially found here, on Bohemia Interactive Forums[forums.bohemia.net] (thanks to Pokertour)

Like getting a plane/chopper to fly over a zone (in a straight line).
You can find in the function viewer (bar at the top>"tools">"function viewer">"A3" and something "ambient flyby")

• Create a trigger
  
• Condition : "True"
  
• On activation
  
  [[X1, Y1, Z1] ] ,[[X2], [Y2],[Z2]],[altitude above ground in meters],"[speed]","[vehicle's log]",[side, ex: WEST]] call BIS_fnc_ambientFlyby;
  XYZ 1 are the initial coordinates from where the aircraft spawns. XYZ 2 are where they'll be heading.
  Do not write "X Y Z", just the numbers (to find them, they are the number at the bottom left hand corner, they correspond to the placement of your mouse in the 3d editor or on the map)
  Speed can be: FULL, NORMAL, LIMITED.

Video from which I initially learned it:
2/75 Ghost Platoon's Eden Editor Tutorial for Ambient Fly-bys | Arma 3 |

Videos and guides that may help you besides the ones that will be quoted throughout the guide. These can show several useful things.
You can also find a mod list to help you in your mission making mission (I'm sure it's grammaticaly correct).

Guides:

• Greytega's "Arma 3 Eden Editor - Scripts I use often"
  A list of scripts similar to my guide but by a guy way more skilled. I must say I don't really understand everything but it's a cool reference.

Videos:

• OperatorDreswki video "How to make awesome ARMA 3 missions" (21 minutes long)
  Basics of the multiplayer respawning system, and how to use the MCC mod (mainly as Zeus) and Ares
  https://www.youtube.com/watch?v=8PRfhQLU5HM

Mods:

• -=MCC=-
  Great mod, it allows you to generate more or less random missions after having started your scenario, switch into Zeus mod, generate multiple things (like airdrops). Basically, it does the job for you in no time, and allows you to modify a lot of things ingame. Great for quick mission making when you have friends with little to no patience.
  
  
• Achilles
  This mod is really awesome. Evolution of the Ares mod, it allows you to greatly customize AI behavior, and introduces a lot of features to enhance your scenarios (smoke pillars as an example).
  
  
• 3DEN Enhanced
  A mod that simplifies the eden editor in the scenario making. Awesome for single player mission making for the animations, but really sad that it doesn't help you put animations for multiplayer

I don't care about the likes or favourite, I think it's more a way to keep the guides in your history.

But what I really like, is feedbacks. Don't hesitate on sharing your opinion, thoughts, and corrections (pour mein pobre english), and if you feel like I should add/know anything handy

1. Place the object you want to use as the "vehicle spawner"
2. In its INIT, copy the following (watch out there are things to modify)

Things to modify :

• The name players will see when interacting with the object (change the "Open Garage" in between the " " for what you want)
  
• The _pos. The vehicle will spawn on the position you input here. To get the coordinates of where you want to spawn the vehicles, right click on the ground and just copy and paste them.

Each time you use it, the script will create an empty helipad that will be used as a virtual garage. Watch out : spawned vehicle can collide, so just spawn one at a time !