[gizmoduck]

If you're starting from scratch, as other users have mentioned, the READMEs, CONTRIBUTING, etc. are all good sources.

After that, take a peek into the Issues. Many people open bugs and/or create pull-requests to resolve something. It's quite plausible that you can gleam a lot of information from what's going on behind the scenes from these; especially, if they're open-source projects with a lot of public consumption.

If it's in a language I don't understand (presumably because I have never had the need to use it), I'll try to write the basic "Hello, world!" apps or something slightly more complicated, just to get the gist of the language. The helped a lot with Rust, for example.