For carving, three different types of knife are used, in a 'three stage' process: first cutting the lines with the main carving knife (toh), next removing wide unwanted areas with the round chisels (marunomi), and finally trimming away waste close to the printing areas with the small flat chisels (aisuki).
First stage: cut the lines of the drawing, holding the knife at an angle that will produce a beveled edge on the finished line (Fig. a). Keep the tip of the blade about 1 ~ 2mm deep in the wood.
Second stage: switch to the round chisel, and start gouging away the waste wood. Only the waste lying within about 5cm of any printing area will need to be removed. You should aim to create a 'valley' around each of these areas, with a depth that varies with the distance (Fig. b). Hold the chisel firmly in one hand, and with the other use a mallet to drive the chisel through the wood. Change direction as the grain of the wood dictates. Do not carve right up to the outlines previously cut with the toh, but keep a short distance away.
Third stage: trimming with the small flat chisels. Pare away the remaining waste wood, working from the areas already cleaned up by the marunomi right up to the carved lines (Fig. c). Work in short strokes, with a slight 'scooping' motion. Be extremely careful when moving along the lines - any spots where the toh didn't quite cut deeply enough are in danger of splitting away at this point. If you feel resistance - stop and re-cut the line a bit deeper at that point. (This is a very common trouble spot for beginner carvers ...)
When this is all done (Fig. d), it's time to move on to the next step - cutting the 'kento', the registration marks.