There are a number of Youtube videos that demonstrate the Slide Lock ruler. They helped me understand how it is different from regular rulers that have a handle.
I use my Slide Locks as in the videos. However, I also use them on top of other rulers -- something the videos don't show. This is probably because of liability concerns. In other words, I will prepare as if I am going to cut with one of my regular rulers, and then just before cutting I place the Slide Lock on top of the ruler and press down. It keeps my hand up and away from the cutter and it also helps keep the underneath ruler in place while I cut. I even do this with my June Tailor Shape Cut mats! I place the Slide Lock just to the left of the cutting slot I am using, moving the Slide Lock for each cut. I find this helps keep the mat from sliding around.
Edit: There are others, but here are a couple of links to Youtube demonstrations of the Slide Locks:
https://www.youtube.com/watch?v=hYOoRetnlfM&t=106s
https://www.youtube.com/watch?v=e-VKvtILhKE&t=54s