It consists of using a needle to stitch up hundreds and hundreds of little stitches to form the lace itself.
Work is generally started by securing the main, heavier guiding threads onto a stiff background (eg thick paper) with stitches that can later be removed. The work then in a variety of stitches - the most basic being a variety of blanket stitch. When the entire area is covered with the stitching, the stay-stitches are released an the lace comes away from the paper.