Antonio, if you just use the code from https://gist.github.com/codearachnid/4705028 only and put that into your theme’s functions.php file it will modify all events being imported to your blog’s timezone settings from the PAC offset. There is no need to modify anything other than inserting this code.
I am not sure what theme you are using that does not have a functions.php file (that is default functionality for WordPress themes). So I would recommend referring to your theme’s documentation for where customizations should be placed.