I just build a box, but not able to change its height. Please teach me how to modify the dimension of the object after I built it .Thanks!
Try using _SolidPtOn for solid editing.
I would simply use sub-object selection (Ctrl + Shift) and use the Gumball to move the face of a box. It’s probably the easiest way.
Here is the link to a tutorial video that explanes it very simple and a lot more for starters.