How to apply a Drupal patch with Ubuntu

The patch utility is by default installed in Ubuntu. All you need to do is to download the patch and to apply it. Provided that the patch was made relative to the root directory of the concerned project, navigate to the that directory (using cd). For a patch on Drupal, that will be the Drupal directory; for a contrib module or theme, that is the root directory of the project.

Once there, issue the command:
patch -p1