You don't absolutely need a central repository for Git. It's decentralized. You can learn the basics (committing, branching, rebasing, amending, merging, resolving merge conflicts) entirely on your computer.
My advice would be to get familiar with using Git locally first. Simulate things like merge conflicts - have two branches that both change the same line in a text file, then merge them together and resolve the conflict.
Once you're more comfortable with using it locally, learn about code forges like Github or Forgejo.