How do I see which tables are busy without walking the floor?

Two places. Settings → Tables & QR ordering marks a table Busy now. On a POS machine or a waiter phone the Tables screen is the room itself: white is free, dark has an open tab, amber means they have asked for the bill, and a green outline means the guests ordered on the QR code themselves. Beside it a panel counts tables open, the money sitting on them, and the longest open table.