Now description.ext is a VERY important file for this, well I will say this if you don't have it in your mission folder this will NOT work.

To start you will need to find your mission folder, traditionally this is in C:/documents/Arma 3 - Other Profiles/*your profile name*/missions/missionname.island it is on
When you find this double click on it and you will see a mission.sqm folder, this is your mission in code format, DO NOT TOUCH this unless you know what your doing.

Now right click in that folder and go down to New and then Text Document. Name it description.ext
Now I am going to tell you a problem I had when I first started doing this. There is a bar on the that has home, share, view (windows 10) click on view and to the right on that bar should be show file extentions make SURE this is CLICKED, if it isn't you will name it description.ext, but the system will think it is description.ext.txt. This will make the code not work. For windows 7 out of memory you go into the top bar and then on file I think there was a properties and somewhere in one of those menus there is show file extensions.

Lets begin putting the code in.
First it will be structured like this,
//cannot be read so you can put whatever behind them.
//tells the game that it is the ORBAT config
Cfg ORBAT
{
//The name you call it, this is not case sensitive
class main_nato
{
// The number eg. First
id = 1
// 0 = numbers 1 = Roman Numerals and 2 I think is Alpha, Bravo, Charlie ect.
idType = 0;
// West = NATO, BLUFOR {BLUE}. East = CSAT, OPFOR {RED}. Resistance = AAF, Independant {GREEN}. Civilian is self explanitory{PURPLE}. Unknown again self explanitory{YELLOW}
side = "West";
//A picutre under the writing, MUST BE 512px 256px
insignia = "path/file.jpg or png or paa,";
//Size of the unit
size = "Platoon";
//type of unit
type = "Helicopter";
//name of commander
commander = "Allen";
//Rank of commander
commanderRank = "General";
//name of ORBAT %1 is the id, %2 is the type, %3 is the size
text = "%1 Echo Squadron";
//short version
textShort = "%1 Echo";
//Whats the color of the ORBAT, side color used if it is 0,0,0,1. USES Red Green Blue Alpha
colorInisgnia[] = {0,0,0,1};
//the description, could include what they are doing or something
description = "Tasked with eating buritos";
//what units it controls (no brackets)
assets[] = "(look up arma 3 Config vehicle class names}";
//whats under it
subordinates[] = "main_tank";
};
class main_tank
{
// The number eg. First
id = 1
// 0 = numbers 1 = Roman Numerals and 2 I think is Alpha, Bravo, Charlie ect.
idType = 0;
// West = NATO, BLUFOR {BLUE}. East = CSAT, OPFOR {RED}. Resistance = AAF, Independant {GREEN}. Civilian is self explanitory{PURPLE}. Unknown again self explanitory{YELLOW}
side = "West";
//A picutre under the writing, MUST BE 512px 256px
insignia = "path/file.jpg or png or paa,";
//Size of the unit
size = "Platoon";
//type of unit
type = "Armored";
//name of commander
commander = "Allen";
//Rank of commander
commanderRank = "General";
//name of ORBAT %1 is the id, %2 is the type, %3 is the size
text = "%1 Echo Squadron";
//short version
textShort = "%1 Echo";
//Whats the color of the ORBAT, side color used if it is 0,0,0,1. USES Red Green Blue Alpha
colorInisgnia[] = {0,0,0,1};
};
};

Now to show it on the map go into the ingame editor and then once inside go to modules, then strategic/ ORBAT markers place that on the map somewhere and click on it. Inside should be Cfg ORBAT path and Cfg ceiling path. Now put into Cfg ORBAT path of them: missionconfigfile >> "CfgORBAT" >> "main_tank" this will be the subordinate then put missionconfigfile >> "CfgORBAT" >> "main_nato" this is the top path. then click ok and play the mission, it should come up somewhere with a marker that is interactable when you click on it it should open up an area that shows the path, congratulations you just made a ORBAT marker path.
Thanks for reading also if you have any questions just post in the comments what they are and I will get back to you as soon as possible.

(should look like this, this is a different one to the one we just made)
This is a very cool feature I forgot to add, it allows a red cross to go through the orbat, like it has been destroyed.
The code:
{ [ _x, "mil_destroy", [1,0,0,1], 1.2,1.2,45 ] call BIS_fnc_ORBATAddGroupOverlay; } forEach [ MissionConfigFile >> "CfgORBAT" >> "*yourorbatclassname*" ]; put that into a trigger and vola, when you activate that trigger it destroys it.

https://community.bistudio.com/wiki/ORBAT_Viewer
Everything in that webpage can be swapped, it is also explained as well on that webpage ORBATs, if my explanation is unclear, this may be more cleared.