After you graduate , you serve 2 years to get your FULL GMC Medical Licence to practice in the UK.
If you have intentions of going back to the USA or somewhere else , then you don't have to bother doing the 2 years at all. You can do your internship etc..... in the US or wherever and use that to practice here.
But bear in mind , here in the UK , we will not give you help with the USMLE. You prepare for that yourself. But I am sure you know that. Providers like Kaplan can help you with that
Anyway : The 2 years after graduation form what is called the Foundation Programme. You spend 1 year in your F1 Placement , this is where you get to practice in a clinical setting and are a doctor and whatnot. You get paid for this. After the F1 year you go into F2. This comes with a bit more pay and will give you a chance to choose your specialism.
Then after your F2 year , you then go into whatever speciality and will be called a "Registrar" then after that you have a Consultant.
But before we think of Consultant and Registrar , let's not jump before we can walk
Hope this advice helps you
edit: SORRY I JUST READ THE OP CORRECTLY NOW!