As options guidelines can be enabled and disabled. There is no option to add guidelines neither help about it.
Guidelines are there to help you align elements to each other.
Try the following: On an empty canvas add two boxes, and change the size of one of the boxes. Then start dragging the smaller box around the larger box. Now you'll see that the guidelines will appear when the edges of the boxes align, or when the center of the boxes align.
This can be very helpful when you have multiple boxes and you want to order them properly. You can then align them using the guidelines.