Look at the handloom. It has over a thousand threads that run from top to bottom. These are called the warp. The weaver had to use the foot pedals to raise every other warp thread (half in total) to make a shed (i.e. a gap). The weaver then used his hands to pass a shuttle, carrying one thread (called the weft) through the shed. The upper warp threads were then lowered and the bottom warp threads raised so that the weaver could pass the shuttle back through the new shed.
Kay introduced a stick or leather strap. This was attached to cords so that instead of using their hands to pass the shuttle between the warp threads, the weaver could jerk the stick from side to side to make the shuttle speed back- wards and forwards through the loom.