Hi I have a nephew who is now 2 years old. He has recently been put up for adoption. It has gone through the courts that the child is being adopted and the mother and father cannot him until he is 18 and that is if he chooses to find his real family. Does this mean that I cannot see him either?

Yes, that means you cannot see him either.

IF the adoptive family chooses, there may be contact with the biological family. However, an adoption means that all legal ties to the biological family are severed, and you have no right to any contact.

Does it have to go through the courts if the adoptive family chooses we can have access or can they choose there and then?

The adoptive family can choose to do whatever they want. Once the adoption is final, they are the legal parents. So they do not have to go through the courts to allow or deny anything.

I have never experienced anything to do with adoption so I don't know much about it.
At the minute we get to see my nephew once a month for 2 hours and he then goes back to his foster parents. Could it be that the foster parents could adopt or do they only foster?

Sometimes foster parents do adopt.

Once the adoption is final, the adoptive parents can choose to cut all contact.

As noted, normally many foster parents just foster, and once a child is adopted they leave that family to the adoption family. Some foster parents do adopt if that is what they are looking for.

But it is completely up to the people who adopt.