representation of what your lens sees. "D" just designates "Digital" as opposed to a
Now you may ask; "Why do I want to look through a viewfinder? My point and shoot has a LCD on the back which essentially does the same thing." Ever try to look at that LCD on a bright sunny day with the sun behind you? Or shoot down at the beach with all the sand reflecting onto the LCD? Pretty impossible isn't it. By using the viewfinder on a DSLR you isolate your eye from the sun and get to see exactly what your image will be with no distraction. The first advantage of a DLSR.
DSLRs also allow you to change lenses as opposed to the lens on a point and shoot camera which, while capable of being zoomed, cannot be changed for different specialized lenses. There's the second major advantage!
DSLRs also have a larger digital sensor than point and shoots. With that comes better quality, and lower noise. So even if you find a point and shoot with the same 10 megapixels as a DSLR, the quality will not compare. The third advantage.