As someone else has already stated, don't try to take the keg apart unless it's leaking (and thus needs to be fixed) and also is completely depressurized.
You'll need a sankey type fitting to connect to this thing. Have a look
here at the 1st and 3rd pictures on the page. You'll have to determine exactly which type you'll need. The larger orifice, pointing straight up, is for liquid out, and the smaller one on an angle is for gas in.
To drain it, simply hook up your CO2 to the gas in connector, and your beer line & tap to the liquid out. The connector, with its handle up, gets screwed onto the keg. When it is locked in position, you move the handle down toward the keg to push the keg's spring-loaded closing mechanism down into the keg, thus opening it. To remove the connector, pull out on the handle, then move it up away from the keg to disengage the keg opening mechanism. Then unscrew the connector.
To clean it, you'll first have to depressurize it (bleed pressure off of the gas in fitting). Then pour some water straight down into the connector's liquid in fitting. Disconnect, slosh, reconnect, drain. Same to sanitize. To fill, just hook up your racking hose to the liquid in fitting and either let gravity take over (if your fermenter has a tap) or just suck on the gas in fitting to start a siphon (if racking from a carboy).
Once you get the proper fitting and play with the keg a bit, the whole procedure will become obvious. The nice thing about sankey fittings is that they're all threaded - I find them much easier to disconnect/clean/etc than simple barbed fittings. Hope this helps.
