The patches/plugins will need to be applied to RC on the server (it wont matter if its PC or MAC), hopefully who ever made the solution you choose will have provided installation instructions.
To apply a patch you need the patch utility installed and then you can run a command like `patch -ul -d /path/to/roundcubemail/ -p1 < /path/to/patch` to patch your copy of the code. Sorry but I cant really be more specific until I know which filtering patch/plugin you are using.
If you are using RC 0.3b you might want to try one of the plugins from here
Plugin_Repository ? RoundCube Webmail they are easier to install than patches.