Let's do this step by step.
1. on the Create tab on the right, click 'Box'
2. go to the viewport, now you're about to create a box.
3. DRAG, (do not release your click!) from one point to another.
4. at the desired place, you LEFT CLICK, only once.
5. drag your mouse up to draw the height and click again.
If you hit Esc, or right-click anywhere along these very short steps, it'll just exit the operation, and it'll not work.