Spinnakers can be a lot of fun. As noted above there are two types-
Symmetrical and asymmetrical.
If you're just cruising or casual day sailing or short handed an asymmetrical can be considered. The tack is usually attached with an adjustable pendant to the stemhead, either in front of or behind the headstay. The pendant is used to raise or lower the tack depending how it's being used. The pendant is let out, raising the tack and opening up the luff when going down wind and lowered when the wind is on the beam, tightening the luff so to use the sail more like a headsail. The clew of the sail has a sheet led back to a block near the stern and then to the winch. When gibing the clew is usually brought around the outside of the headstay to the other side. It can be done with one sheet and just moved from one side to the other or with two sheets like the jib. No pole is used with an asymmetrical and there is not much extra hardware needed.
A symmetrical spinnaker on the other hand needs more hardware and a little more learning, but they're more fun too. A symmetrical has to be flown with a pole. You'll need a pad eye on the front of the mast to attach one end of the pole, a line attached to a bridle on top of the pole to hold it up and fed through a block higher up on the mast and if possible led back to the cockpit and another line hooked on a bridle on the bottom of the pole and fed through a block below it on the deck then back to the cockpit. This setup raises and lowers the outboard end of the pole which is hooked to a line attached to the tack of the sail. That line is led back to a block near the stern and then to the winch. Pole higher downwind and lower as the wind goes forward. The clew of the sail has a sheet run back to a block near the stern and then to the winch, on the other side, of course. The tack and the clew change when the spinnaker is gibed. The pole now on the other side of the boat and attached to the other corner, which is now the tack.
The sails can both be used with the wind forward of the beam but not as much as the headsail. It can be exciting using the spinnaker like this as it can develop quite a bit of power as the wind picks up.
Launching and retrieving the "chute" are also things to consider.
Most of the major lofts have info and instructions on their websites:
http://www.na.northsails.com/Home/tabid/1907/Default.aspx
http://www.hood-sails.com/
http://www.quantumsails.com/
http://www.doylesails.com/
To name just a few. There are many more.
Rich