I would probably start with a good sized chunk, about a softball or a little bigger, try to knock off a chunk and try to process it down a little. I wouldn't go straight for trying to make something if you a lot of rock on hand, just practice the techniques. If you're short on rock or have to buy it I would try to get smaller chunks that are made by knappers, or are of right shape, so you don't waste a lot of rock practicing.
I started on plate glass from windows and started with making arrow heads. I've never tried a biface or knife blade etc. yet.
yeah, im not too good at the jargon yet either