Personally, I would advise finding an itch to scratch - something you'd like to see improved. Then try to understand the code from this perspective - where would you put the functionality, which pieces would it be connected to? Try to follow the lead, make notes as you read the code. You'll eventually get a feel of the infrastructure, going from the deal to the big picture - this is my default way of navigating projects.
If at any moment you feel lost, look through related issues and merge requests, as well as Git history. Perhaps you'll see how things get changed in the project, patterns intrinsic to it.
Also, keep in mind that you can always try to contact the community/author or invite someone to try figuring out your goal with you - once you collaborate, you'll get a solution tailored to the way you think. It does engage other people, but it also makes coding social and (at least to me) more satisfying.
If at any moment you feel lost, look through related issues and merge requests, as well as Git history. Perhaps you'll see how things get changed in the project, patterns intrinsic to it.
Also, keep in mind that you can always try to contact the community/author or invite someone to try figuring out your goal with you - once you collaborate, you'll get a solution tailored to the way you think. It does engage other people, but it also makes coding social and (at least to me) more satisfying.
Let me know what you think of this approach!