It's a big task to read the entire source code in one go. Reading source code "in the abstract" is hard work.
Why not pick some aspect that particularly interests you. For example: coin allocation, or the user interface for the address book, or block discouragement, or whatever. Then explore that part of the code.
Better still, find a change you'd be interested in making. That forces you to get to grips with that part of the code.
Oh, and have you even compiled the source code yourself? That's the first step, and it can be an interesting and educational experience in itself (especially on Fedora or Red Hat where you'll need to overcome some dependencies). Even if you don't plan to make any software changes, the building the application will help you become familiar with its files.
Let's just say I come up with goals too big for my own good. I will probably end up settling for something small at the end of this.
Yeah, I'll compile it first. That's pretty essential.