If you’re just wanting to install MusePlayer:
You DO NOT need to bother with building the project from bitbucket. You can install MusePlayer by running the installer on this page. You should see a Download Tools For Mac button at the top. It’s also available for Windows/Linux.
If you genuinely wish to build the project:
You’ll need to create a bitbucket account, and set up SSH key authentication. This page has good instructions for it.
Alternatively, you can edit the .gitmodule file to have it update over HTTPS instead of SSH, and then run
git submodule sync. This post has more info.