Form G-325A is required in connection with most green card applications, whether it accompanies the initial visa petition or a later adjustment of status application. The form is available for free download on the "G-325A Biographic Information" page of the USCIS website.
The data collected on Form G-325A gives the U.S. government information with which to check the U.S. petitioner's or immigrant applicant's background. Most of the form is self-explanatory.
If you really can’t remember or are unable to find out an exact date that the form asks for, enter whatever you can remember, such as the year. Alternately, you can simply say “unknown.” However, it is not advisable to do this too many times, or USCIS may return the entire application for another try. Since the questions aren’t numbered, we refer to them by the approximate block.
Blocks 1 and 2 (Family Name, etc.): Self-explanatory.
Block 3 (Father/Mother): Self-explanatory.
Block 4 (Husband or Wife): Self-explanatory.
Block 5 (Former Husbands or Wives): Self-explanatory -- but very important to get right, particularly if the green card application is based on marriage. The U.S. immigration authorities want to make sure that all previous marriages were legally terminated, and don't show any pattern that points to possible marriage fraud in this case.
Block 6 (Applicant’s residence last five years): Be careful here; these addresses need to be in reverse chronological order, starting with your most recent address and working your way down the last five years. For example, if you now live in Detroit but lived in Ann Arbor before, your Detroit address would go on the top line. Practice making this list on another sheet of paper before you enter the information here.
Block 7 (Applicant’s last address outside the United States of more than one year): This may overlap with one of the addresses in Line 6. That’s fine.
Block 8 (Applicant’s employment last five years): Again, be careful to put this in reverse chronological order. If you have been unemployed, self-employed, a student, or were a housewife or house-husband, say so here. In other words, try not to leave any period of time unaccounted for.
Block 9 (Last occupation abroad if not listed above): This line asks you to list your last overseas employment, if you did not already list it under Line 8. People tend to overlook this line, because it is so tiny. Make sure you do not accidentally skip over it.
Block 10 (This form is submitted in connection with an application for): If this is being filled in by a U.S. citizen or resident petitioner, that person should check “Other,” and write “in support of [spouse's or other family member’s] I-130.” The immigrant should check “Status as Permanent Resident.”
Block 11 (If the applicant's native alphabet uses non-Roman letters): A person from Russia, China, Japan, or Korea, for example, would want to fill this in using the native writing script.
Block 12 (The dark box): This is not for signatures; you simply print your name. You would have an A number (Alien number) only if you had previously applied for a green card or certain other immigration benefits, or been in deportation or removal proceedings.