Here are some tips for bevel cuts with a Dewalt miter saw:
First off, a bevel cut is a a cut that is made when the blade is at a 90 degree angle to the fence and is tilted at an angle, anywhere from 0 to 45 degrees. A single bevel miter saw will tilt in 1 direction up to 45 degrees and a dual-bevel miter saw will allow the user to tilt the saw in either 45 degree angle. A common stop besides 45 degrees is 33.9.
To begin, move the slide fence on the saw. Modern miter saws have a fence that will support up to a 90 degree cut and still allow the saw blade and motor plenty of clearance. You should be able to adjust the fence to ensure that it doesn't get in the way of your cuts. Test it by pulling the saw into position and move it as needed.

Regarding the angle of the cut: Many miter saws have a built in bevel scale (looks like a miniature protractor). These are ok for roughing something in but the lines are so close together that the width of your blade may exceed the distance between lines and make it hard to read. If you are working on stuff that is high-visibility, get an angle guide that will line your saw up correctly; they come pre-built with the right angle. Simply rotate your saw to match the angle of the guide.

If you are cutting a lot of wood, over time you will notice the wood you are cutting tends to "drift" out of position. This is pretty common with any saw. A nifty trick you can try is to put a piece of self-adhesive sandpaper under the wood. You can also lock the wood in place with a stop block.