Currently there are two options to do this on Openshift. Probably everyone will meet the web console interface first, where one can specify the location of an existing source code repository which will be copied and used for the application. There is also an input for the branch or tag (or SHA) if the head of master is not adequate.

The second, less known solution is to use the rhc ( Red Hat Cloud) command line tool.

It has a --from-code option and you can also specify git ref however I didn’t find this in the documentation. Simply append your branch, tag or SHA after the git repository, followed by # character.

$ rhc create-app myapp php-5.4 --from-code https://github.com/nick/myapp.git#9fbfc057

Be aware that there is a bug which makes this parameter ignored if the name of branch contains / character.

Both methods send requests to the Broker via REST API. You can read about what happens when you create an application here, thanks to Filirom1.