"Yalla" is the magical button that confirms a ride's details and makes it happen.
Once you tap "Yalla", the Careem app will search for a Captain and match you with one who will be on his or her way to you immediately.
Once you tap "Yalla", your Later booking will be confirmed. A Captain will be assigned to your booking in advance to ensure he or she arrives at your pickup location on time.
Note: You can cancel a Now Booking without a penalty within 2 minutes of tapping "Yalla", and up to 2 hours before a Later Booking's pickup time.