First off you need two of them for them to have any use. Place one directly next to an energy storage (usually MFSU, this dude EATS energy and you can't connect them via cables) and another where you want the other end to be. If it's a one way portal, you only need to power the one sending you, otherside you need to power them both if you're using it to go back and forth. Then, craft yourself a Frequency Transmitter (1 copper cable and 1 electronic circuit, shapeless) and right click the two portals with the transmitter to link them together. Stand on the teleporter and give it a quick redstone pulse and you're off! It takes EU depending on distance traveled and how much you're carrying in your inventory.