Hi Anna! The wonderful team at GitHub (a COSS company) put together this resource: opensource.guide/starting-a-project/
Hope this helps you on your journey into the exciting world of OSS!
IMHO it's ironic that GitHub preaches about the superiority of FLOSS but then ... doesn't make GitHub itself FLOSS. Like wth.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.