Mozhi,
When you set Delivery, closing/settling a ticket will return you to the customer screen
When you set A-la Carte, closing/settling a ticket will return you to the tables screen
With no options set, it shows open tickets and allows you to start a new sale or select an existing sale and add more items or settle.
You can close both screens and start entering items without a table or customer, and this is used for cash sales like at a bar.
If you move a ticket/items it is assigned a new ticket number, but if you click change table then you can select a new table. If you have created a new ticket, you can assign it to a table or customer and it will retain it's ticket number.