That doesn't sound dumb at all, we all have to learn sometime!
A sucker is typically an undesired offshoot from the main
tree. You'll often find them near the ground (sometime it looks like they are
growing directly out of the ground) but sometimes they are up on the trunk a bit and they look like a young misplaced branch that is just sucking onto the main
tree. They'll also typically be smaller than an inch in diameter. You can look at just about any
tree out in the world and see suckers everywhere, and now that you know what to look fo you'll see them everywhere.
Usually they are undesired due to strange growth locations and they'll mess up to look of your
tree in the short term, but if you are inclined to start an entirely new
tree they work great! Good luck!