3-point plugs = household style mains plugs you mean? if so, they are 240AC sockets and totally different to 12V DC that your battery provides.
Inverters? Question is what Mains (240AC) devices do you want to run in the van? Knowing that will help get you the right advice.
I strongly recommend whatever you end up doing, you get someone to fit it for you and maybe watch and ask what they are doing to learn some more for the next time.