Definitely get The ABCs of Reloading if you can. I suggest also Lyman's and there's a lot more information on the web that is useful. There are sites entirely specialized about reloading, and surprizingly enough, even Wikipedia has a relatively good first primer article. Check the articles about internal ballistics too, it will give you an idea of what you are getting into when reloading and what you must pay close attention to. Reloading is not dark sorcery (much), but it is not for the careless!
Like others said, what equipment you buy will depend on what you intend to do with it. I skipped right over buying a single stage press because I knew I'd need a progressive press anyways. But I for sure have been using my press as a single stage while learning the ropes, making sure that every single step is understood, correctly set up, the results measured, adjustements properly made and the final results controlled again before I fiddled with any next step in the assembly chain.
Is the case resized right? Is the primer at the proper depth and set straight and firm? Did I bell/expand the case enough, not enough, too much? How confident am I that I have thrown the correct amount of powder in there? Am I getting the same exact amount every time from the measure? Are the bullets seated too far in or too far out? Am I taper crimping too hard, enough or not enough? What the heck did I forget this time?
I've sacrificed some commercial ammo and made them into dummies just to have cases, spent primers and bullets to play with. I compare the final product with other rounds from the same box. The salvaged powder I'm not planning to use because there's no telling what it actually is and what its characteristics are. At best, all I could do with it is reload the old rounds with the same amount I got from them, that's it, no fiddling without real load data.
And I'm still reading all the while on proper bullet seating, cartridge OAL and taper crimping, chamber peak pressures, powder burn rates, you name it. It's a fun hobby, but it's also a rather technical one. But fun, in part precisely because of that.