Drupal - How do I apply a patch file?

Here are a few links that may help you learn more about patching:

• Applying a Patch Manually
• Making a Drupal patch with Git (also covers applying)
• HowTo: How to apply a patch to a contributed module - Beginner's version (Windows)
• Apply Patches on Windows (more methods)
• Apply patches on Mac OS
• How to apply patches for Drupal modules and files

There's a description in every module under the tab version control. Scroll down to the title "Applying a patch" to find a description about applying patches with git.