Sumayyeh,
be sure that the tracker is on ( the small yellow box on the toolbar on top)
if it is on you can just enter any number while you are drawing.
or you can use the coordinate box ( Window > Palettes > Coordinates)
and no such thing as depth, after you save it as a wall or a beam, when you draw it in the floor plan that would be the "depth".
Read this
http://www.archicadwiki.com/Creative%20Uses%20of%20Complex%20Profiles