Tips when using the Line tool:
To draw a straight horizontal or vertical line the click start point, hold Shift, and draw.
Before you release the mouse, if you move the mouse you can rotate the line in multiples of 45 degrees.
Each line you draw will create a new layer. If you have many such layers you might want to merge them into one. Then if you need to move an individual line, roughly select it with one of the Lasso or Marquee tools and activate the Move tool to move it. This technique applies to the other Shape tools as well.