Dead conifer wood is best. Dry aspen is just as good. Cedar is great. Hardwood is terrible for kindling. Birch bark is great but birch wood is almost always useless for fires.
Conifer wood tends to repel moisture with it's pitch.
Hold it vertically with the lower end on a solid base. Since your sheath knife will probably strike this base it should be wood to protect the edge rather than rock or dirt. Place the blade of your knife down on the top end and with another billet, used as a mallet, drive the blade through the vertical piece until it has split. The knife blade must be larger than the diameter of the billet being split. This way you can hammer it all the way through by hitting it's tip.