The 300 grit is used for damaged and blunt knives and the 600 grit is used for fine honing.
The steel can be used in two ways, firstly the tip can be placed firmly on a surface then the knife blade at a 20° angle can move downwards with gentle pressure for sharpening. Alternatively, the steel can be held in an upright position again moving the knife blade at a 20° angle downwards carefully lightly pressed against the steel.