Yarn and hook: DK yarn and a 4 mm hook (UK 8/ US F) for the circle and sport yarn of your choice (I love working with Tango and Phil Cotton 3) and a 3 mm hook (UK 11/ US D) for the rectangle.
The best effect is achieved by using more colors /shades of the same color. Mind that you can use whatever yarn size/weight (and relevant hook for that weight) you have at hand; that will only influence the size of your circle or rectangle – hence smaller weights of yarn will yield smaller circles/rectangles, heavier weights will produce bigger/larger ones.

Other: Tapestry needle for weaving ends.

Stitches in American terminology: chain (ch), skip (sk), chain space (ch-sp), stitch (st.), slip stitch (sl st), double crochet (dc).