1. Go to the repository you want to clone (something like: https://bitbucket.org/username/repo)
2. On the top menu, choose Repository -> Import repository
3. In the Old repository section, enter the source (CodePlex, Git, Google Code, Mercurial, Source Code, Subversion) and the URL
4. In the New repository section, enter the Owner, the repository name, the access level

(note: each one of the sources in step 3 has different inputs that needs to be added, in our example, we are focusing only on Git)