To add to what spinner said, in the US almost all teas are black teas unless they are labeled otherwise.
Other common types of teas: Green, White, Oolong, Herbal, Rooibos. (There are a few other types that are hard to find, but you'll probably not encounter those). If you grab any tea on the shelf, if it does not say it is one of those 5 types, it most likely is black tea.
Not that I recommend it (because of added sugar or chemicals), buy if you order tea at any restaurant, fast food place, or fill a cup at any convenience store -- they almost all will be black tea, or as most places call it "tea".
Follow up: Are you looking to drink hot tea or iced tea? And are you looking to drink a small amount like a cup a day, or are you looking to use it to replace something else you drink (such as sodas as an example)?