Attendees usually join your event by entering a code, or by scanning a QR code in the mobile app. See the event preview screen for more information about this.
However, attendees can also join your event by using the GPS on their phone.
For this to work, you need to give us the address at which your event is taking place, and draw a polygon around that location. If attendees are within this polygon, then can join your event simply by selecting "Use my location" from the menu inside the mobile app.
You can assign multiple polygons to your event if required, e.g. for events that take place in multiple locations simultaneously.