Many repeaters share the same pair of operating frequencies, but because they are so far away from each other, they don't normally interfere with each other. The resulting confusion can make for some interesting long distance contacts. You will often hear hams refer to a certain repeater that has tones on it. What they mean is that the repeater has a feature that enables several things to happen. Check with the local hams to find out which repeaters have these features.
Many repeaters also have the ability to detect tones on the input as well.
If your radio can transmit these tones it will open the repeater's squelch at a much lower signal level than normal. This is particularly helpful when you are mobile and working the fringe areas of the repeater. You may hear these features referred to as PL tones. It is well worth the few minutes invested to determine if your radio has these features and which repeaters support tones. When listening to the local repeater the new ham will be greeted with all sorts of strange terms.