Not 100% sure if you want directions for making a coaster, or the design. Coasters would be easy enough to make. As for a spider design, I'd just look on line until I found something the wifey would like, print off however many copies you needed, with a few spares - just in case. Cut the designs to fit the coasters, glue down with some good wood glue, I happen to like Titebond II for most of my work. Then you can apply varnish, shellac, or whatever finish - I often just use a coat of thinned Titebond II, which works nicely - altho does tend to have a yellowish cast. For a whiter/clearer finish white Elmer's wood glue, thinned, should work fine. The coasters themselves can be as simple, or complex, as you want them. Squares, rounds cut out with a hole saw, whatever your imagination wants.