Add OpenShift application name after rhc ssh. For example, if you use app-domain.rhcloud.com, then execute rhc ssh app.
If you have not saved authenticate token on your local machine, you will be required to input password. Authenticate token can be saved with the command rhc setup.
This is the way to use ssh without rhc.
Execute the ssh command on bottom right of OpenShift Web console. Or, execute rhc apps and you can find ssh item like AAAAAABBBBBCCCCCCDDDDDD@app-domain.rhcloud.com, then execute ssh command with its argument, ssh AAAAAABBBBBCCCCCCDDDDDD@app-domain.rhcloud.com.