After the immigrant visa packet is received, you need to pay the Immigrant Fee for the Green Card. The beneficiary will not receive the GC when he/she arrives in the US if this fee is not paid.

Payment of the $165.00 Immigrant Fee can be done online at the USCIS Electronic Immigration System (ELIS) Website

While waiting for the arrival of GC, beneficiary can also wait for the SSN to arrive in the mail (if chose to apply in the form). If SSN does not arrive within a few weeks, follow the guides on How To Apply for SSN.