On the next screen you will be able to give the area a tag (Make it unique) and also you will be able to choose between Exterior (terrain) or an Interior (tiles)

The next screen allows you to choose the size of the new area by either choosing the size on the right hand side or by moving the sliders on the left hand side and/or bottom.

Sizes:

Tiny = 4 x 4

Small = 8 x 8

Medium = 16 x 16

Large = 24 x 24

Giant = 32 x 32

Now click finish and your area is ready to build on.

When you click on finish, have a look at the white lines in the grid. This is the boundary of your area. Anything you make outside of these white lines will just be background, and the player won't actually be able to go there.

TIP

You can also get to the Area Wizard by clicking on right clicking on the screen under the Area List on the left side and then left click on Add.