If you're looking at VWs then the model designations usually differ between the UK and Ireland, In the UK it's something like S, SE and Sport where in Ireland you get something like base, Comfortline and Sportline. You'd need to be an expert in small print to work out the exact details between UK and Ire spec. as they won't be the same. On a Passat I'd expect them to be close-ish, on a Polo/Golf less so.
Pique's spot-on : base models will be exactly that (although I think you get a reasonale amount of kit on it these days), SE will often include leather trim, cruise control, bigger alloys, maybe upgraded audio, Sport will usually be bigger wheels again, lower/harder suspension, quasi-sporty seats.
DSG is a VAG double-clutch preselector auto box, very good but maybe a little bit unproven. It's also used on Audis where it's called S-Tronic. FSI is a direct-injection petrol engine - ultra-low sulphur petrol only.
SSE