Hi mike, for drawing on surfaces just make sure to enable "Object Snap" in the bottom toolbar so that it's highlighted in orange. When it's enabled there will be an "on surface" snap that will place the current point onto a surface. And if you want the object that you're drawing to follow the direction of the object that you placed the first point on (like drawing a rectangle directly on the side of the cube), make sure you are placing those points inside of the 3D view, not the Top/Front/Right views. When you do the drawing in the 3D view it will automatically align planar drawed objects onto the surface you are placing points on, when you're in the 2D Top/Front/Right views it keeps the drawn object flat to that 2D view.

For some more information and small example video captures, check out here:
http://kyticka.webzdarma.cz/3d/moi/doc/V2releasenotes.html

look for the section labeled "Drawing / snapping on to surfaces".

- Michael