What you're describing is making a template from which to extrude a part.
This is actually selecting two points and creating a third point halfway between the selected two.
Example.
Selecting points:
select point 1 - click on it, it turns white, and press the space bar.
select point 2 - click on it, it turns white, and press the space bar.
Adding the 3rd Point:
Part-> Add Point (or shortcut CTRL-A)
this adds a third point halfway between points 1 and 2.
To keep adding points, unselect the first two points (Shortcut: Shift-U) and repeat as needed.
Yes, in gmax you could do a shape merge (less messy) or boolean cut, but this is FSDS
