Creating a gitlab account is free. The paid part is when you create a project or something. To access CASToR gitlab, you only need a gitlab account.
It is fine being a beginner, it means you can learn! Which is also why I tried to show you how to fish at the place of giving you the fish. After all, “Give a man a fish, and you feed him for a day. Teach a man to fish, and you feed him for a lifetime.”.
See the discussion in Problem in crystal index to find two possible solutions.
Good luck!