On your dashboard, choose the service your want to use from the three tabs (GitHub, Bitbucket or Self-hosted Git repository).
You'll see a big green button saying New Project, just like the one below:
If you've already linked a GitHub or Bitbucket account (if not, have a look here Linking with Github/Bitbucket), simply choose a repository you want to start tracking, choose a branch and click Start tracking. codebeat will now start analyzing every commit you push to this repo and reporting any problems with it.
If you're using a self-hosted repository, please have a look at the section Using codebeat with a self-hosted repo.