I'd read the link that Cad64 gave you about using viewports.
A quick explanation of using viewports in paperspace:
You draw whatever you are drawing in Model space, at full size. (A full size car, house, planet, or whatever it is).
You have your drawing border in paperspace, the same size as the particular paper size you want to use.
You put one or more viewports within the drawing border to 'view' the modelspace, setting the scale of the viewport to fit/view whatever is needed.
You plot the paperspace at 1:1 on the same size piece of paper as the border size. (or 'scale-to-fit' to fit it onto smaller paper sizes).
So everything is drawn actual size, the only scaling is done by the viewport. (Unless you also want to plot a large sheet size onto a smaller piece of paper).