When viewing the table plan you can open a new tab on a free table by pressing on the table and selecting 'New Tab'.
You will be presented with the new tab screen where you can specify the name and number of covers.
You can also optionally specify a tab owner.
When you have entered the details press 'OPEN TAB' and you will see confirmation the tab has been opened. Then press OK.
You will see the table you have opened the tab for is now highlighted in blue to indicate that it is occupied and displays the tab name and number of guests at the table.