Hiya @Mishka. There’s some information found here that you can look through:
http://discourse.stonehearth.net/t/teach-me-to-mod-blush/14144
Some points of interest from there is:
- Look through an existing mod to get an idea of how it works.
- Start small. Having plans for an ambitious mod isn’t bad, but not something you’d want to start with when learning how to mod.
- Modding tutorials made by @voxel_pirate.
- Learn Json. You can make most simple mods by overriding or mixinto data through json files. Also, use jsonlint to make sure that your json files are valid.
Speaking of overrides and mixintos. this blog post gives a pretty solid explanation of how they work (and of a few more things).
There are also some other tutorials and guides around the discourse on how to mod certain things into the game. Just search for tutorials and you should find most of them.
As @jomaxro said: good luck! 
