How to draw board outline in ADS?

You can draw PCB outline working in ADS layout.
If ' cond ' is your metal layer,select say 'default' layer
to mark your PCB boundary.

Should I use a rectangle to represent the board, or use wires to draw the outline?

If you are making PCB boundary to mark board edges for cutting the PCB
after fabrication, you can draw four corners in metal layer itself.
If you want to pre-define your PCB size while making a layout,then draw a
Rectangle in some other layer.

I'm sorry, I still don't get it...

I want to know how can I draw the board edge, which can be exported to gerber file to cut the board during the fabrication.

I guess I can draw a hollow rectangle using wires in some other layer and then just export it.