Woodcut is an ancient printmaking technique dating back at least 1200 years. It's made by gouging a flat piece of wood, then rolling ink over the remaining high points of the wood (the surface not cut away). You work essentially opposite to drawing with ink: the parts cut away are the white portion of the print, what's left are the black lines. I use mainly U-gouges (named for their U shape), V-gouges (ditto) and knives to cut my blocks of wood.
You have to remember to sketch your image on the block of wood in reverse because the actual print will be a mirror image of the wood block.
Tools of the trade
Close up carving with a U-gauge. The high (uncarved) surfaces have been rolled in ink for illustration purposes only.
A brayer is used to roll on thick black oil-based ink. The ink is only caught on the high surfaces of the wood block. The white areas, or lower surfaces, have been cut away.
Thin (ie Mulberry) paper is then laid on top the inked woodcut and the relief is rubbed on to the paper with an smooth object or run through a press.
For the last several years I've been fortunate enough to be able to use the large rolling presses at Peregrine Press.
The piece of paper is removed and voila! Your wood block print is complete. I prefer one more step though (see below).
I then wash my prints with egg tempera This is by no means a standard practice, but something I've grown to enjoy as a way to add uniqueness to my work.