There are two ways in which to assign bookings to Tables/Areas in your Diary grid.
Drag and Drop - click on the booking bar in the grid > drag to the relevant Table > unclick to drop the booking into the new table
Alternatively, you can use the Bookings List in the left-hand side panel:
> There will be a button with the Table number/name the booking is placed in or if they haven't been placed into a table yet this will display an arrow icon > click on the button > this will now display 'Done'
> If they are already assigned a table, this row will turn purple. To change the table to another one, simply click on the table row they are in (the purple will disappear) and then select the table row you want to put them in (you can select multiple tables, turning them purple)
When happy with your selection, select the 'Done' button again and it will save them in the table(s).