If you have some awesome code in your
functions.php-file, and want to be able to deactivate it without having to erase the code, or just want to share it with other WordPress-users, you can add a few lines of code to make a plugin out of it.
Put your code in a separate file and add it to
wp-content/pugins/, and add the code in the top of the file.
Then go to Plugins in WP Admin and activate the new plugin!