This follows on from the Split Tool

CAUTION DO NOT MAKE CONCAVE BRUSHES USING THIS TOOL

A concave brush are things like arches L shapes etc this picture below shows why

As you can see it try to fill in the gap and it usually looks a lot worse when in game

This is also why you should use split instead of carve I have never used carve once but I assume it will create concave brushes. If you want concave brushes Import them from 3d studio max or Maya

Ok
Have you map loaded etc now make sure your in Selection Mode

Place you curser where you want your first point to be then press V now place second point press V again until you loop back to your first point again join it up by placing cursor on the first point and pressing V.

Now you have sealed the 2d brush this will pop up

Now just give it a depth value hit ok there you go a 2d brush

There you go nice and easy, as long you don’t create concave brushes

Barkey

Download this tutorial