I am totally confused.

There are tons of tutorials telling me how to install forge.

But not a single one tells me how to install "addons" into the Forge dev environment.

 

Can someone come up with complete steps?

So you want to know how to setup your addon development environment?

 

Here is an easy(probably easiest) way:

Just make folder named 'libs' in your project directory and put the mods on which you want to build addon.

Then just 'gradle setupDecompWorkspace eclipse' (or idea, if you are using Intellij)

So should I put in src, dev or api version, if any?

So should I put in src, dev or api version, if any?

Mainly api is for those who want compatibility,

and dev is for those who want total addons. (AFAIK)

 

Anyway You have to check the mod documentation, since there could be some exceptions.

Download the API, and put it in src/main/api. Then you can use it in your code. You don't need to anything special when building.