How to view/edit only original mesh after subdivide modifier

I am following a tutorial to make a glass.

After creating the basic shape and mesh, in the tutorial he uses subdivide modifier. He doesn’t apply it yet. Of course when you do this, the mesh is gonna get divided into smaller faces.

In the video, however, I am not sure how he does, he still manages to view the original mesh and work with it. I don’t know how to do this. All I see it’s the smaller faces, but can’t view the original mesh.

How do I do it?

Try this button, additionally you can hover over most things with your mouse to get tooltips.