Every so often a portal opens beside a player, and anybody standing nearby can go through before it closes.
When one opens
Any map with players moving about can get one. The portal opens a few steps from somebody, a banner goes up for everybody on the map, and a line appears in the System chat. Event portals have a colour no other effect in the game uses, so you will know one when you see it.
Get there quickly
Stand on the portal or right beside it and step through. If nobody goes in, it closes after a short while. Once whatever is inside has been dealt with it stops letting people in, even if there is time left.
Who can go
Anybody standing close enough. You do not need a party, and you do not need to be the player it opened beside. You cannot go through from inside a dungeon, while you are already in another event, or in the middle of a trade.
What is on the other side
Which event you get is rolled when the portal opens, and some are rarer than others. It might be something that came through and needs clearing out, somebody waiting with something to say, or a store room nobody has opened in a long time.
What it pays
Finish it and every player who went through gets the full reward. Nobody has to split it, and events are one of the places Charge Dice come from.
Getting home
When the room is done, a way home opens inside it. Step through and you are back exactly where you went in, facing the way you were facing. You can leave before that too, and you land in the same spot.
Hang about too long after the clear and you are sent home anyway. Drop your connection and you have a little while to get back before the room lets you go. Die in there and you wake up somewhere safe, as you would anywhere else.
Next: upgrading your gear.