This video is exactly what you want. Skip past the jig part to minute 2:00 - just setup miter saw correctly. Did my whole house from it...Make a few templates and use these as a guide - you only need 4 - inside left/right and outside L/R.

https://www.youtube.com/watch?v=c1MIi6v34_o&list=WL

Without using math or any sort of miter saw, the essence of getting corners to meet is to hold the crown in it's installed position (albeit like on the kitchen counter against the blacksplash). Then make your cuts at 45degrees. For inside corners it is easier to cope the connections, and on a long run you do the inside corner first if the same run also has an outside corner.

Thank you for your help. i tried and tried. Gave up and returned it. Its impossible get a straight or even cut with scissors. Even a sharp knife wouldnt work. It wouldnt go thru the sticky tape on the back. If i removed the tape lol it stuck to everything. This stuff might work for craft projects or framing but not what i wanted. im going to try the more forgiving pvc type trim. No painting, cuts easy and can sand it down to make a near perfect fit. Thanks again for answering.