If I'm correct, any sockets that are white (or brass) in your van will be 240 volt mains sockets for when you have a hook up. 12 volt sockets are a light brown colour.
There should be a switch somewhere to switch on your 12 volt system, and I would imagine a zig unit so that you can switch it to charge your leisure
battery as you go along.
In terms of getting mains power out in the wild you can use an
inverter as mentioned above, but running anything more than a mobile or notebook computer will VERY quickly drain your leisure
battery as this is what an
inverter is connected to. The easiest option is to buy a generator (preferably a silent one), or you can have a large bank of batteries charged by
solar panels, but I think at this point in time that may be getting a bit complicated for you.
With a generator you simply start it up, run the mains lead into your hook up, switch on your mains and you're away. When we run ours (very frequently - it hardly uses any petrol) we always try to wait till people have gone, or if they're staying, make a point of going over and saying we're putting it on, but if the noise annoys them at all just come and knock and we'll turn it off. Not once has anyone said they could even hear it!