I use open source self hosted software everyday. I love the community and I would love to be able to contribute to some of these projects.
As far as code goes, I basically no nothing about how it works. I see the development section of the repos I use and again, I’ve go no idea how it works.
How can I teach myself how to offer small improvements to the projects I use?
You could look through issues raised by other and try to replicate it. Offer your voice to confirm that there is a concrete issue, logs, steps to replicate, etc. As your familiarity builds you’ll be able to identify likely areas in the code causing the issue. This really helps others to implement the fix and before long, you’ll be the one fixing it yourself.
Also, look at codetriage.com.