This is how you can add parties on a smartphone:
Click on the "+" sign at the top right corner of the screen.
Click on Walk-in or Waitlist.
Decide on the party size.
Decide on the area (if there are any areas set up).
Click on Seat now.
Choose the table where the party will be seated (table coloured in orange is the one that the system chose).
Click on the orange checkmark at the upper right corner (Confirm).
You have now successfully seated a walk-in.