Hey there,
I have been a hobbyist programmer for quite some years and have a few smaller projects under my belt: mostly smaller GUI applications that have a few classes at maximum, make use of one or two external libraries and are very thoroughly documented and commented.
Since I love the free software movement and philosophy, I wanted to start contributing to projects I like and help them out.
The thing is, the jump from "hobbyist" to "being able to understand super-efficient compact established repos"... seems to be very hard?
Like, looking into some of these projects, I see dozens upon dozens of classes, header files, with most of them being totally oblique to me. They use syntactic constructs I cannot decipher very well because they have been optimized to irrecognizability, sometimes I cannot even find the starting point of a program properly. The code bases are decades old, use half the obscure compiler and language features, and the maintainers seem to be intimately familiar with everything to the point where I don't even know what's what or where to start. My projects were usually like four source files or so, not massive repositories with hundreds of scattered files, external configurations, edge cases, factories of factories, and so on.
If I want to change a simple thing like a placement of a button or - god knows! - introduce a new feature, I would not even remotely know where to start.
Is it just an extreme difficulty spike at this point that I have to trial-and-error through, or am I doing anything wrong?
There's a lot of great advice here already; I've got one more piece from trying to figure out GIMP a few years ago.
Read the old commit notes and implementations. Treat them like your favorite soap opera. Get emotional about it; have your heroes and villains.
By the time you've gone from 1998 to 2015, you'll have a thorough understanding of what's going through everybody's heads when they look at the code.
You know what, that sounds super enjoyable. I'm going to do that.
Now thats the spirit!