On the page that pops up, you have your virtual floorspace, as well as some buttons on the right hand side of the screen:

Adding a table

1. Press the create table button to add a table to the screen

2. Drag the table to wherever you wish

Deleting a table

1. Click on the table to select it

2. Press the delete button

Once you have finished arranging your tables, press the Save/Exit button to commit the changes.

Note that after clicking the Save/Exit button, you must then exit the table mapping screen, and then come back to it before you'll see the changes you've just made.