I realize that not everyone has the opportunity to go squidding, but you may be able to get some whole squid from the fish market which you will need to clean and prepare. Hopefully, the youtube video helps.
Tips on how to clean and prepare squid.
If you are not squidding, because then you will not have a choice on what squid to look for, the size of the squid will affect your cooking. Thick mantles or the steak part will result in a tougher meat. Look for thinner, younger and smaller squids which will be the most tender. Also, if you are purchasing squid from a fish market, look for squid that have bright eyes rather than eyes that are opaque and sunken in.
Different cuts for different applications
Squid rings
This shape is commonly seen for deep fried calamari. The rings are formed when the mantle of the squid is cut cross-wise to form rings.
Squid steaks
Calamari steaks are made by cutting the squid down the center of the mantle and flattened to form a steak. It is best to tenderize these calamari steaks by marinating them in an acid of either buttermilk, lemon or lime juice or a water and baking soda solution to break down the muscle fibers. It can be further tenderized by scoring.
For Chinese cuisine, cut the scored mantle into 1 " x 2 " bite size pieces. For stir-fying, score the interior side of the mantle to allow the squid piece to curl and result in a tubular shape.