Our app currently supports booking a ride for up to 6 people in Arlington. When setting your pickup or drop-off location in the app, just tap the - or + button near the top of the screen to indicate how many people are with you (e.g., if traveling with two friends, choose "+2"). You can also tap the "1 Passenger" tab above the place pins to add riders.
You can read more about pricing for extra riders here.
(Note: our app does not currently support different drop-offs for riders traveling together, so just make sure you're all going to the same place!)