The prior responses are right, but there's a little more to the story.
Z-PC, aka "Fusion", is a correcting polish. It is like a swirl mark remover in its ability. But there is also another mildly abrasive polish in the line up (Z-AIO) that I'll describe further down.
Z-2 and Z-5 are sealants that you apply in very thin coats, wait for them to dry, and wipe off. Z-2 has a brighter finish, and is great for white. Z-5 has a "deeper" finish and claims to fill slight imperfections, though most of us on this site don't use it for that purpose (and personally, I can't see any filling). Some folks use Z-5 as a first layer, then put Z-2 on top to get the benefits of depth and high gloss. But either product is excellent all alone, with conventional wisdom being that dark colors getting more from Z-5 and lighter colors get more from Z-2. But even spending three sentences on the difference between Z-2 and Z-5 might be overstating the case.
Z-AIO and Z-CS are relatively new products in the Zaino line. Z-AIO is an all-in-one type product which has some chemical and abrasive cleaning ability and also lays down some protection. It is a good finishing process after using Z-PC, but on its own is a good paint cleanser and prep product that creates a good base for the sealants to bond.
Z-CS ("Clear Seal") is a wipe on and walk away sealant (no residue to remove). It was the first successful such product to come to market. Some folks use the "tripletts" of Z-AIO, then Z-CS, and maintenance with Z-8 (which is a spritz and wipe spray, sort of like detailing spray on steriods). Others, like myself, are still experimenting by using Z-2 and Z-5, then gliding on a coat of Z-CS. Z-CS is claimed to be even more durable than Z-2 and Z-5, which is quite a claim since the classic Zaino sealants consistently test among the most durable on the market in third party tests.
The Zaino line up is a great one both because each of the products is among the best in its class, and because it now has lots of choices to suit personal choices on process and type of product. Those choices can also make it a bit confusing. You may want to start with an order of the Tripletts, along with the car wash, if you are looking for an easy, durable process. On re-order, consider getting one or both of the classics sealants, Z-5 or Z-2.
BTW, the Tire Gloss is really great both for tires and trim, and if you are already paying the postage....
If you have any specific questions, maybe I can ask if there is time. 
