A few words before I delve into the details: if you here reading and you haven't watched Fate/zero yet, you should go do so; it's a great use of forty-seven minutes (all forty-seven of which are needed in order to give a proper introduction). Second, while Fate/zero is the prequel to Fate/stay night, you don't need much knowledge about it. It does help to be familiar with the series (preferably the visual novel), though. Let it be said, though, that Fate/zero is completely watchable without previous knowledge of F/SN (especially when the DEEN adaptation does little justice).