Matted cat hair!

I have a short hair indoor cat. He's about 6yrs old. On his back there
is about 4 or 5 little clumps about the size of my thumb. It's matted
and tangled. I tried to use a brush and comb but ts just too tangeled.
Im thinking about trying to wash/shampoo it out. Last but not least I
guess I can cut it out. Any ther suggestions? And does anyone have
info on how matting happens? I dont understand. One day his fur looks
great and next day I find clumps of matted hair. Maybe I need to brush
him regulary.