Use relative coordinate input. Example: To draw a rectangle block 30 x 800 do this:
- click on rectangle icon or type rectang in command window
- you will be asked to specify first corner, so click somewhere or type x,y coordinate (for example: type 100,100 and hit enter)
- now in command window type @30,800 and hit enter
To arrange objects in space, I recommend you to draw some help lines. Start POLYLINE (pline in cmd window or icon on the left), click on the end point of the first object, then enter @50,0 for next point of polyline to get horiz. line with length of 50 (click ESC or right mouse button to finish polyline). Now click on MOVE, select the second object, pick line's start point as basepoint for the MOVE, then pick line's end point for destination. That's it.
Also, there are video tutorials at
http://www.babacad.com/tutorials.html (english) and
http://www.babacad.com/tutorials_de.html (deutsch)