Yep ... the pipeline to becoming an open source developer:

1: Use open source software.

2: Get annoyed by some small, incredibly specific bug.

3: Fix that bug yourself.

I've fallen victim to that a couple times personally.

And @TotallyWorthLife -- it doesn't take a whole lot of knowledge, as long as you're working on a project that's willing to humor beginners' mistakes. I contributed to OpenRCT2 and KDE, both written in C++ ... and I know basically zero C++. (I only knew a bit of Python and some half-forgotten PHP.) But I knew enough to look at the source code, ask devs questions about which files do what, and understand the code enough to zero in on the issue I was experiencing. In both cases, I ended up asking more experienced devs there if I'd gotten the changes right, but in both cases, I actually had. (Admittedly, one of those cases was basically by pure luck. They were using bitwise operators, which I knew nothing about, but I'd copied the line from elsewhere in the codebase where similar operations were done, and it happened to be the right one.)

Just two pieces of advice I'd have for starting out:

1: Look for something that should be a very simple fix. In both of my cases, I only needed to change one file, and only a couple lines in that file.

2: Look into fixing a bug, not implementing a new feature. Or, at least, if you want to add a new feature, you should definitely be talking to that project's devs first to see if they even want to implement that feature, and if so, get their advice on how they'd want to implement it. Yes, you're doing free work, but if you're adding more code for them to maintain and then expecting them to maintain it, you're kind of demanding that they do free work as well. A simple bug fix, though, is a one-and-done that should (at least in theory) reduce the amount of maintenance work the regular devs of that project need to do.