How to Open a Gateway
If you have Hereafter stones in your inventory you need to open your Teleport book, select the location you want to go to, and press the little greenish circle near the bottom right corner of the window. This will start the summoning timer for the gateway and once formed you just need to jump through (literally).
However, unlike the recall skill, you will need to use a Hereafter Stone to open a gateway. You can buy Hereafter stones from the auction house or you can make your own. It takes one Hereafter stone to open a gateway that leads to a location on the same continent and it takes three Hereafter stones if you are traveling to another continent.
A trick to save a Hereafter stone if you are going from the west to the east is to teleport to Sanddeep Community Center, use the gateway right outside the center towards Rockborne Basin, and then teleport again from that location to your final destination. This should end up saving you a single Hereafter stone for the trip.