How Do You Cut Crown Molding A Miter Saw?

Most radial arm saws have a degree setting on them. Not all walls are perfectly angled, so you would have to take that into consideration. I'm not very good with a T-square.
You could use a miter saw.
I put crown molding in my house and found some of the walls to be out of square. That can be a headache. I found at the Home Depot, in the molding isle, they have corner cornices that you nail into the corners and butt the molding up to it. This eliminates the need to miter the corners and it looks really nice. All you have to do is stain them to the color of your molding. They have inside and outside corner cornices and they are very inexpensive. About two dollars each.
I'm no carpenter, hope this helps.