How does one get started with contributing to OSS?

I always read articles about how it is beneficial to write open-source software to improve one's skill, but even though I want to do that, I still can't find projects that would be welcoming for a "beginner" (it's not that I am new to coding, but I've never done any work outside of college or coding competitions), so how do you guys find something to contribute to, and has it improved your skill?