Here is what I understand about simplex and repeater modes. Bare with me as I am still learning. Channels 1-7 are not used by repeaters. Channels 15-22 can be used in simplex but can also be used by repeaters as receiving. Repeaters are setup in frequency pairs. Lets say there is a repeater in your area that you have permission to use. You have been informed to use 462.550. To properly access that repeater, you would need to set your radio to the given frequency, set the repeater shift direction to a + then set the frequency offset to 5MHz. If provided a PL, this will also need to be programmed. End result, when you press the PTT button, traffic is transmitted over 467.550 to the repeater. It will then take that transmission and send it over the 462.550 frequency. Anyone that can listen to that frequency will hear your traffic but will not be able to respond unless they a repeater capable radio with the proper settings in place.