Removing Material/deleting material

The quick and dirty method is to just use an assembly cut to remove the unwanted side.

I do this sort of thing for quick images of how something would look or for a quick presentation.

Generally you want to avoid assembly level features like cuts created in the assembly. If that's not an issue, create a sketch in the assembly and use the Extrude command with the Remove Material option. You can make the cuts visible at the part level, but be aware that creates an External Reference from the part to the assembly (which you generally want to avoid).

If you open each individual part, you can select a datum plane and use the Solidify command to remove everything on one side or the other of that plane.

If it's just for visualization purposes, you can create a cross section using a datum plane or planar model surface.