Green card application

[FYI]

Hi there,
My son has an SSN, he went to school at the Buzz Aldrin School in Reston.
He is now 25 and wants to work in the US with Goldman Sachs. He does not have a green card, because he has been living abroad.
How does he apply for a green card?

Would it be beneficial to use an agent, if so can you provide some names Please?

[jnk]

YOu meant he gave up his green card while staying abroad. In that case you have to apply all over again or he can come to USA on H1 visa.

Using an agent will not make any difference.