The basics first: the stances, the basic forms of a blow, and the parries to counter them.

The general form of the art will be apparent very quickly: light and rapid movement, crouches and jumps at need, quick switches from foot to foot or hand to hand, full use made of the ease with which a walking stick can be whipped about for feint or for a hard blow. (Enjolras, admittedly, is a slim and rapid-moving man, and his style tends that way in any case -- but it's not as if Harry has bullish size and strength either.)

Harry's general athleticism and balance and forearm strength should stand him in good stead, anyhow.