Need some basic assistance

How do I set up a 36"X24" drawing in paper space,? the software defaults to 81/2" x 11'. How can I bypass the default and draw a 36x24 box into which I can add my viewports?

I'm sure there are other ways, but all I do is change the paper size in plot settings and hit apply to layout, then cancel out and the area you selected will change, then you can resize your viewports