What camera part is this?

I recently got a Nikon d3200 kit and I don't know which part this is or what it does

That is not part of a Nikon D3200 kit. You can find out what comes in the box here: http://www.nikonusa.com/...D3200.html - mouse over "what's in the box".

The power plug looks like the kind you use in a two pin shaver socket - like the kind we have in the UK

That is probably an adapter to the charger. Nikon's chargers are universal. Depending on the country it is going, Nikon includes different plugs for the charger so you can plug it into the wall to charge.