I guess you mean draw lines from the laast coordinates to the new one?
then add a few global variables:
lastX=""
lastY=""
# and modify
lastX=""
lastY=""
def click(event):
global lastX, lastY
if lastX != "":
c.create_line(lastX,lastY,event.x,event.y,fill="white")
lastX = event.x
lastY = event.y