A fork is a git-side copy of a repository and is independent of the repository it was cloned from.
A branch is a version of a repo that represents changes. Branches are generally used for developing code.
The command 'git branch' returns a list of branches that indicates the current active branch. It can also create a new branch from an existing branch when fed the appropriate command line arguments.
The git clone command clones a remote repository to a local machine.