What happens if you have already booked a trip and somebody wants to join you? How can you add them to your existing booking?
You need to access your trip page. You can find it under My Trips. Click on the trip name.
You are now on your trip page. Find the green "Select" button in the upper right area of the trip and click on it.
The following pop-up will appear:
Just click on "Book Again" and proceed with the booking as usual. Add as many people to the booking as needed.