3" CD Singles are really unique things because of their size and scarcity. They sit snuggly inside the moulding in a CD tray, and play like any other CD.
Japanese ones in particular are really cool - they come in a flat "snap pack" format. You break off part of the pack, and fold the packaging up to make a small 3" CD case. The Japanese detail is great, often featuring the lyrics of the songs in Japanese and English. These pictures show the singles I have, some of which have been snapped and folded up, and some which are still in their original flat pack format. Scroll down to see individual photos of each.