The smart applicant will submit their I-90 electronically. That is not always possible, so you may also mail the application to the correct Service Center (see the form instructions for details).
Get the Receipt Notice and Gather Evidence Regarding Your Current Status
Now that you have your receipt, you may now make an appointment at your local CIS Office, using the Infopass system, to get a stamp in your passport, or a temporary green card showing that you are currently a lawful permanent resident of the US.
Wait, Wait, Wait, Wait for Your Green Card
At some point you will do your fingerprints and the green card will come in the mail. Eventually. Six months to a year is the norm.