What are they?
Mods allow people to add anything to a game. You literally can add ANYTHING. (Well, almost anything.) Do you want a tree in space? Well you can have a tree in space. Do you want the BatMobile? Well you can have it! AND DO YOU WANT ALIENS? Um... I don't think there is a mod for that, but maybe there will be soon!

• Add content
  
• Allow things to happen
  
• Add in a super cool plane you saw online
  
• Add new parts, so that you can build more things
  
• Add in new planets

And a lot more!

Mods for other games may be, but for KSP, mods will not jail-break you're game, get you in trouble, or anything like that. Its just adding new content!

Finding a mod isn't too hard. There are lots of mods! A few websites I reccomend for them:

• Kerbal Stuff[kerbalstuff.com]
  
• The official mod page[www.curse.com]
  
• The forums[forum.kerbalspaceprogram.com]

Also, remember, certain mods will tell you if it is compatible with the current update! So make sure that the mod is compatible with 0.90 or whatever version you are using!

Once the mod has downloaded, read the next sentance.
MAKE SURE TO INSTALL ALL MODS THAT ARE SHOWN ON THE MOD PAGE, OR THE MOD WILL NOT WORK! What I mean by this, is that lots of mods require you to install other mods. If you do not install them, the mod will not work. To find the mods required, just go to the page where you got the mod, and look for Required mods or something similar.

Most mods will have a .txt file. Open it if it does. Read and make sure you have installed everything correctly. In the folders that you have downloaded, there should be another folder called "Game Data". We will need this. In order to install the mods, You must get into the steam files or the ksp files.If you do not know how to do this, please look it up, as there are different ways for different systems. Once you're in the KSP folder, there should be a folder that says "GAME DATA". In there, drag the files from the mod folder (Inside the mod folder, go into the "Game Data" folder, and select all files from that folder) into the KSP folder's Game Data. DO NOT DRAG THE MOD GAME DATA FOLDER INTO THE ACTUAL GAME DATA FOLDER. DRAG THE CONTENTS OF THE MOD GAME DATA FOLDER INTO THE ACTUAL GAME DATA FOLDER. Once thats done, run KSP.

IF EVERYTHING WENT RIGHT, IT SHOULD WORK!

You have successfully downloaded and installed a mod! Go have fun!

NOT WORKING?

Watch a video on it to make sure you did everything right.
For example:

If you want to install a craft, follow this!

1. Find the craft
   
2. Download the craft
   
3. Make sure it is a .craft file
   
4. Go into the KSP folder, and find the ships file
   
5. In the downloaded folder, there should either be a SPH or a VAB. If there is both, do this for both of them: Drag the contents of the SPH and or VAB into the Ships folder in the KSP folder.
   
6. It should work now!