This video goes through the process of finding a patch from the Drupal.org issue queue, and then applying it to a contributed module. After testing the patch and confirming that it fixes the bug, we then walk through the process of reporting back that the patch has been reviewed and tested by the community and is ready to be applied to the module's main branch. This video will show you how to clone a Drupal.org project, but it assumes that you already have git installed and are familiar with the basics of using git.
Here's more information on how to set up your command line to show the git branch release context.
For instructions on creating a patch and submitting it to Drupal.org, watch the Creating a patch for a module video.