All menus are customizable in the Manager-Configuration screen so placement of items on the tabs and menu can vary per company.
A list of options will appear under the item after it's been clicked. To remove the item click the red "-" sign.
The item will be removed
To add an item to an open order simply click on the item you wish to add from the menu screen and it will appear on the order. However if you want to increase the quantity of an item already on the order click on the item you wish to add to.
A list of options will appear under the item after it's been clicked.Click on the green "+".
The item will increase in quantity.
Once an order has been saved, items must be voided.
To learn how to remove an item from a closed ticket, you can read the How To Void items from tickets articles