Let's say I have a little tent shape, like this:
I've decided I want the bottom segment to follow the diagonal angle of the top segment instead of being vertical. I could grab the bottom four vertices and move them along the X-axis like so:
I could also delete these vertices, and select those above them then grab or extrude along the angle. The problem is, I don't know how to do that! How can I lock the grab/extrusion to continue on along the angle of the tent?