In Codebase you can review and comment on code pushed to a repository, for example straight from a commit or when reviewing a merge request. To add a comment to a commit, simply navigate to a particular commit either from the Dashboard or your commits list:
Now from within the diff you can hover over a given line of code, which will bringup a comment icon. Click the icon to bring up a comment field, type your comment and press Post Comment to save it.
The comment will then display within the diff as you have entered it for your team to review further.