how to make a bent line with arrow head in a dia diagram

if you want to make an arrow line from element to another, use "polyline":

 click on the element you want the line to go *from*:

then click and drag the arrow head over to the element the arrow is going to point *to*. when the element turns red, unclick and it will snap to the element:

right click on the new line and choose "add corner":

you'll now see an orange box. click on it and drag it to where it creates a nice L shape: