This is just the disconnect, you'll need some method of controlling the beer once this is on.
Barb takes the 5/16 Beer line as a push on fit
If you just put it on the barrel the beer shoots out all over the place. You can use a pub type bar tap but you'll have to adapt it probably. A bit of thinking and a trip to B and Q will usually sort it.
Easiest way is the Flexi tap.
To put it on you pull the ring at the bottom up, push it on the spigot on the top of the keg and allow the ring to spring back and lock the disconnect on.