Yes! To sit with your friend, view the event you are both have tickets for and select "Add Friend." Select your friend from your contacts, and you'll be linked together and will receive seats together for the event.
If your friend hasn't reserved a spot, they will be invited to grab a ticket and then you'll need to tap "Add Friend" again to link your tickets.
Please note, there is a maximum group size you can have for each event. You will receive an error if you exceed the maximum group size.