Some of us may have nipples as adults that have changed dramatically from the way they were when we were younger (maybe because of surgery, or age, or life experience).
Regardless of how many you have, or what they look or feel like, your nipples and the nipples of people you want to have sex with can be sources of sexual pleasure.
The main three zones to consider are the breast, the areola, which is the area around the nipple, and the nipple itself.
If you don't look carefully, most nipples look more or less the same. It's true that most of us have a nipple or two (some of us have three, or more) but we certainly don't all have the same nipples or the same relationship to our nipples.