Quill pens are
writing instruments made from the
feathers of large birds (think
turkeys or
geese). The shaft of the feather was
tempered with heat to make it strong. The fluffy part of the feather is then stripped off, in order to clear a place for the hand to write with. Finally, a
nib is fashioned from the tip with a
knife.
Writing with a quill pen is the same as its successor, the dip pen: dip pen in ink, write until you run out, then repeat. As the nib wore down, a new one could be cut further up the shaft.
Up until the nineteenth century, this was perhaps the most common way of marking paper (or parchment). The metal nib of the dip pen proved to last significantly longer, and displaced the quill.
Sources:
http://www.flick.com/~liralen/quills/quills.html