What part of the squid is edible?
The tentacles and the muscular body of the squid are edible. 

To clean squid, pull the head and tentacles off the body and remove the skin and fins from the body. Turn the body inside-out, remove the central bone, wash out the inside of the body, and turn the body back into its original shape. Cut the tentacles off of the head, and discard the head and beak. Summarized from: Jacques Pepin's Complete Techniques