We have the service manual for this one on our site and it has info on safety, disassembly and parts.
See http://www.microwavedisplay.com/r1380_r1381_sm.pdf
The latch head is the part of the door assembly which has hooklike things protruding from it.
It is held under tension by a spring so that the hooks will push down and activate the door switches while the door is closed.
When the tab where the spring mounts breaks, the switches are no longer activated and the oven will not operate.
It will need a new latch head (and a spring if you lose it! *grin*).
You can order parts for Sharp models from Tritronics at http://www.wehaveparts.com.
William Miller † MicrowaveDisplay.com, March 2007