Cut off a 21-in.-long board for the shelves, rip it in the middle to make two shelves, and cut 45-degree bevels on the two long front edges with a router or table saw. Bevel the ends of the other board, cut dadoes, which are grooves cut into the wood with a router or a table saw with a dado blade, cross- wise (cut a dado on scrap and test-fit the shelves first!) and cut it into four narrower boards, two at 1-3/8 in. wide and two at 4 in.
Google is probably the first place where most people would start searching for woodworking plans, but often the top results can be a mix of articles and how-to pieces that just aren’t detailed enough. Sometimes they’ll link to the plans (like we try to here at Lifehacker), but other times, they’re just showing off a cool project. There are better, more precise ways of finding what you’re looking for.