1. You choose a point at your picture. Let it be the middle of the picture for the first time.
2. You think what you want to draw and where you want it to be. And I know that you want to draw a block. Not a building or fence, just the simplest block you can ever imagine.
3. You draw it letting all the horizontal lines horizontal and vertical lines - vertical, but all the other lines - aimed at the chosen point in the middle of the picture.
4. ? ? ?
5. Success!