clone downloads the whole repository. It contains the current state of the default branch (which should be develop) as well as the changes required to go back to any point in history, and the changes required to switch to any other branch. Note that it only keeps a record of the changes (not the entire contents of each branch or point in history) which is how it can store all this information so small.
To view all branches, with the current branch starred:
To check out a different branch:
git checkout <branch name>
There are tons of simple guides and quick references online for git. I recommend taking a quick look at one of those to get started.