Do you have a trailer? If not, you'll be riding your bike on the street at least some of the time. And for most of us, the street's the beginning and end of our time in the saddle. That means that if you're a biker, you're going to want to know a little something about street tires.
In order of aggressiveness, they run from cruiser, to touring, to sport touring, to sport bike. And generally, along that spectrum, you start with high stability, high durability and high gas mileage, then move toward higher speed and cornering performance with less durability and fuel efficiency.
Be realistic: What kind of riding do you do? What's your skill level? What kind of bike do you own? Answering these questions will tell you where your tires should be along the cruiser/sport spectrum. Then look for the tire that fits your bike's specs in terms of tire width, aspect ratio and rim size. These are the three numbers you see printed on your tire in the format of, for example, 120/70/R17.