To apply a patch to a file in typo3 you have to go to the console of your webserver. Copy the patch file into the directory where the file to be patched is located and use the following command to apply the patch:

patch -p0 class.tx_ttnews.php < class.tx_ttnews.patch 

This example shows the patching of the tt_news extension based on the "full scale news posts in XML feeds" article I wrote.