Modding is quite easy, but hard to explain
Basically, every mod is a folder with a file inside, called manifest.json. This is the file that starts everything, like it lists all objects in your mod and resources necessary.
To have some examples, you can simple open other mods, or the game itself. The *.smod files are nothing more than a *.zip file that was renamed, and inside that zip is the mod folder. So all you need is to rename the file extension from smod to zip and unzip its contents out to check what is in it.