Turkeys are really fun! (In my perspective at least) Before you purchase turkeys make sure you know, and not to mention the people on BYC know what you are going to do with your turkeys, whether it's for meat for thanksgiving, showing, or just having them for a hobby. Probably the best thing to start out with is where are you going to put them? Coop, fields, or backyard? I would look at how many you want and what kind you want, there are 8 standardized varieties of turkey and many more of them, look on Porter's rare heritage turkeys and you'll see. Most of the varieties of turkey are heritage (a more slow growing turkey) and for starts I would start out with only a few but enough to sustain. The best meat birds are the fast growing ones also known as the Broad Breasted's Bronze or White which grow at a rapid pace as a starter I did for and found that to be really expensive, how many you order depends on how much meat you want.
A young turkey is called a poult, a younger female is a jenny, a younger male is a jake, an older female is a hen, and a older male is a tom. You can tell the difference in many ways normally when they are mature enough is when you can tell, Toms strut and their tail feathers spread out while hens tails don't really do that, I have found the calls of the hens to be very different than the toms and in most cases hens don't gobble, toms often have beards and hens may occasionally have one, the color of the head on the tom can change color with it's mood and whether or not it feels sick, and you can tell in the broad breasted breeds when the tom has filled out in the breast areas (the important parts for meat) faster.
Good luck on getting turkeys and if you have more specific questions please feel free to ask.