You use the command line to interact with a local repository where you keep files on your system and to interact with a remote repository where you keep your files on Bitbucket. To perform these actions from the command line, you'll also need in install a DVCS next.
If you'd rather not use the command line, you can interact with remote repositories from Sourcetree instead. Sourcetree is a free Git client for Windows or macOS. For more details, see Get started with Sourcetree.
If you'd like to use the command line with Git on Windows, we'll cover that on Install and set up Git.