How can I add cave molding against the walls in my room?

Purchase a few long pieces of cover molding that stretches from one corner to other as per measurements of your room. Cut the molding for a splice connecting two pieces that converge in the center of a wall. First, you do the inside corners and then follow the same with outside corners. Adjust the saw at 45 degree angle and all the corer angles are in 45 degrees. And each cut is exactly the opposite of the cut you actually want to make. When you are working, fix the cove molding firmly in place and watch the angles. You will be done sooner than you can imagine!!