With this tool draw a line along the item you want to be stright.
Here I put it right on the line of the building.
After you draw the line you can move it and adjust it to the correct position if needed.
When you grab the top you can move the line and it will pivot at the bottom.
When you grab the bottom of the line it will pivot at the top.
If you grab it in the center the line will move side to side.