FOSS gamedev and creative worlds

What's the procedure for code contribution? Someone told me about this project and that it's open source, and since it's a really good idea, I thought I could potentially contribute.

https://github.com/celeron55/minetest The Minetest Engine
https://github.com/celeron55/minetest_game Minetest Game (Block Definitions,Textures and so on)

You can fork them on Github