For example, if you are holding your event in the Kitely Welcome Center, then enter this world's Hypergrid Address in the event's "Where" field:
grid.kitely.com:8002:Kitely Welcome Center
If you wish, you can enter the world address in the event's Description field instead of the "Where" field. If you choose to do this then the address must be the last thing in its line.
You can optionally specify a starting location in the world by adding the coordinates after the region name. Note that this will only work if the world doesn't have a default starting location set. Here are two examples (with and without a "Z" coordinate):
grid.kitely.com:8002:Kitely Welcome Center/120/130
grid.kitely.com:8002:Kitely Welcome Center/120/130/21
In general, the event description should contain only plain text (not HTML). However, it's possible to include images by using this format (substitute your own image URL):