One end of the board retains it's butt end and simply butts the wall. No cutting. When coping the matching piece, you only cope one way...it doesn't matter if the corner is 85 degrees or 95 degrees. One the end is coped with a slight backcut, it'll fit. The top portion of the coped end can be somewhat delicate, but the beauty of that is that it'll mash itself to the previously butted piece, giving a tight joint. If you're having trouble coping, try tightening the blade in the coping saw, or reversing the blade so the teeth are facing the "wrong way."
Plus, coped joints don't open up with seasonal wood movement as mitered joints may do.
Always glue corners as well...though on a cped end there isn;t much to glue. It does help on outside corners, though.
If you're using MDF trim, don't try to cope it. It'll fracture. With "real wood" trim, practice coping on the end of a long board. You'll only waste a few inches of stock if you blunder it. Practice makes perfect.
A good trim book is the one written by Craig Savage, published by Taunton Press. A search of his name on Amazon or similar will bring up the title. If the $20 book saves you an hour's time and 3 or 4 botched cuts, resulting in several feet of wasted stock, isn't it worth it? Good tips on the number one nemesis of the DIYer, how to cut crown. Good ideas on what walls in a room to trim out first. Fairly detailed ideas on how to cope, and details on how to adjust your second cut if the trim shows a gap after the first cut.
If you want to save money and time, buy the book. Then you can resell it on Half.com for $10. Look on Half.com first to see if it's available, if so, you can get it for roughly $10.
Whether you cope or don't cope, miter or don't miter, use putty or don't use putty, at least try to do the job right from the start. Try for good joints. Whether you're a 30-year trim man or a first-time DIYer, pride in worksmanship should be goal number one.
Enjoy your project...but seriously, think about buying the book. Consider it as another tool in your arsenal.