Registered Angus means the bull or cow is 100% purebred angus with papers “registered” with the breed association. Certified Angus beef is a program where you can market your cattle as “certified” angus if they are at least half angus.  This means one parent is 100% angus or both parents are 50% angus.
A bull is half the genetics in a herd.  You can pay less for your cows.  Put a good purebred registered bull with them.  Then you will have superior calves for a lower overall cost.  If you save heifer calves, you can eventually swap out the bull.  Registered bulls will create better and more marketable cattle within a shorter time period.
Angus cattle come in two colors, black or red.  The gene for black coat is dominant and the red coat gene is recessive.  In the United States, the cattle are registered in separate breed associations, American Angus Association (Black Angus) and American Red Angus Association (Red Angus).  In most other countries black and red Angus cattle are registered together.
EPD stands for “Estimated Progeny Difference” and it is supposed to predict certain traits of a bull or cow based on the information about its parents and grandparents recorded in the breed association database.