This action will bring up a window that prompts the player to make a choice, yes or no, and allows you to specify the choice to make with a tag that you add to the modstrings.txt file. If the player chooses yes, then he will be ported to the specified coordinates. You can obtain the coordinates through the World Editor in the Editing mode, by using the Locate Coordinates option in the Camera menu, when looking at the spot where you want the player to get teleported. It will show you a window with the coordinates of that spot, and you can enter them in the action's fields.