TelePads are pads made out of EnderEssence and some Unstable Minecraft Science that gets emit by crafting tables.
Telepads will teleport any person to coordinates that person has registered. Despite this idea, TelePads do not communicate with eachother, that's why the owner keeps track of coordinates to not end up in the middle of nowhere without a TelePad to teleport back.
Telepads have a built in memory system that keeps track of the last coordinates used. This allows the owner to make a copy of his coordinates must he have lost his original one.
TelePads can be forced to listen to other people. The owner will have to enable that on the pad, and make his friends register the pads coordinates.
(Universal pads have no more downsides since 1.7.2_1.2)
How do they teleport us ? That's a good question. Nobody knows... TelePads take about seconds to load coordinates and 3 to load up and prepare for the person in question to teleport.
That said, they can be accesed over any dimensions. But the end still has a fishy effect on telepads...