How should I prepare for learning C before college?

If your college has assigned a textbook or published a syllabus, use that as your main guide. It will likely match the terminology and topics used in class better than random recommendations online. Supplement it with small exercises, and bring specific questions to your instructor or classmates once the course starts.

Don’t switch resources every time you read that someone dislikes the one you’re using. Most introductory books have strengths and weaknesses, but consistency matters more right now. Build a few tiny command-line programs—number guessing, a calculator, a text adventure, or file-based contact list—then revisit the parts of the book that those projects expose as confusing. Save raylib and larger libraries for when you actually want graphics; they aren’t necessary for learning core C.

Try a small text-based tic-tac-toe game. It’s large enough to be interesting but doesn’t require a graphics library. You’ll need to represent a board, read and validate moves, update the game state, print the board, detect wins and draws, and possibly make a basic computer opponent. That gives you practice with variables, arrays, loops, functions, conditionals, and input without burying you under a framework.

You probably don’t need to panic or master everything before classes begin. Beej’s guide is a perfectly reasonable resource, especially if you’re working through the examples yourself instead of only reading them. Type the programs in, compile them, change things, and fix the errors. Not understanding every detail on the first pass is normal, and having seen the basics before the course starts will already help.