Use the Outer Wilds Mod Manager for downloading, installing, and managing mods.
Outer Wilds is a neat game. Check it out and buy it or whatever.
If you want to make your own mods, the OWML documentation has most of the info you need to get started. The easiest way to start is by cloning the mod template project and following the instructions there. The aforementioned Discord server also has a modding channel.