I don't think anyone got to this question properly so I'll give it a go:
Firstly, the phrasing of your question suggests you have a kinda idea that you've heard of 'Crisis' think it sounds neat, but don't really know what it IS, so ill try to break it down for you. The key thing to keep in mind that there have been three Crisis stories, but they're not REALLY connected, it its not a series per se:
Crisis on Infinite Earths - the daddy of them all. Back in the 80s, DC did this super dense 12 issue mini which took their myriad of parallel universes and blew them all up, leaving the slate relatively clean. It was pretty much the new 52 but in the 80s. The story itself is dense, cosmic, hyperbolic and probably entirely impenetrable if you're not well versed in the old DC multiverse. I've tried to read it and gave up.
infinite Crisis - the more I think of it, the less I'm sure what this was actually about. Firstly, it's not just the crisis, but there are 4 (count em!) lead-in miniseries - a space one, a magic one, a cyber spies one and a villains one. All of which leaves the DCU teetering on the brink of collapse and whammo, the multiverse is 'back'. It's big punchy Geoff Johns comics. I remember it being quite thrilling at the time, all the comics were flowing into this one nexus point, the stakes seemed super high. Big stuff. Maybe less substance than you'd think. This was followed up by the excellent 52 series, where the main heroes were out of action for a whole year. Out of the whole crisis shebang, 52 is what it was all for.
final Crisis - Grant Morrison writes the final New Gods story. Massively cosmic. Impressively self contained bar a few tie-ins by the main writer. Great ancillary series (Rogues Revenge, Crisis of Three Legions, Revelations). My favorite of the three Crisis stories, but lots of other people will disagree. But they're idiots, don't trust their opinions.
I dunno man, I would not recommend Crisis books to a new reader at all, they're all mired in. A really specific continuity from a bygone time, all riddled with plot holes and confusing nuances... But then again,they're something that only comics can do, so you might enjoy them.
