When a U.S. citizen or permanent resident submit a family-based petition on Form I-130, it does not, by itself, give an intending immigrant any lawful status within the United States. What it does achieve for the immigrant depends on the family relationship and where the immigrant is currently living (whether in the U.S. or overseas).
For an overview of the full application process, see How to Get a Foreign Family Member Into the U.S. as a Lawful Permanent Resident.
The I-130 is a Petition for Alien Relative, meant for use by U.S. citizens and lawful residents in order to bring family members into the U.S. as lawful permanent residents (green card holders). The I-130 asks for information that will legally establish the relationship between the petitioner (U.S. citizen or resident) and the person(s) wishing to enter the United States. In other words, if you claim to be someone's mother, husband, or the like, you'll need to be able to prove it!
The form may be filed out for a U.S. citizen's spouse, children (married or unmarried), parents, and siblings; or for a U.S. permanent resident's spouse or children (unmarried).
Once the U.S. petitioner's status and the familial relationship are established, U.S. Citizenship and Immigration Services (USCIS) will likely approve the I-130 and move the case forward for further processing.
Many people make the mistake of thinking that this USCIS approval is the last step in the process, and that the incoming relative is now considered a lawful U.S. resident. But the I-130 is merely the first step in an often-long process. Many applicants will face a waiting period, and for every applicant, there is still a chance that problems will pop up before their U.S. permanent residence is approved.
If the intending immigrant family member lives overseas, then approval of the I-130 will result in the application being transferred to the National Visa Center (NVC) for further processing.
The application might actually have to stay outside the United States for years, if they're in a so-called "preference category" of visa-eligible people.
What's a preference category? It's a visa type that is subject to annual limits on the number of visas (green cards) granted. More people usually apply for immigrant visas every year than the legal limit on how many can be given out. So, long waiting lists have developed. These are often from two to 25 years long, depending on the family relationship category and the country (there are per-country limits). The waiting list is managed by the person's "priority date," or the date upon which the I-130 was first filed with USCIS.
Some relatives are considered "immediate relatives," and do not face this added wait for a visa. Immediate relatives include a U.S. citizen's spouse, parents (assuming the citizen is age 21 or older), and unmarried children under the age of 21. Everyone else who qualifies for a U.S. immigrant visa is in one of the preference categories.
Only after the family member's priority date (if any) has become current and a visa number is available will the NVC transfer the case to the appropriate U.S. consulate.
Near the end of the process, every overseas immigrant applicant will receive further instructions from the U.S. consulate and have to attend an interview before receiving a visa to come to the United States. They will also have to show that none of the grounds of inadmissibility block their eligibility for a green card.
For immigrants who are living in the U.S. when their I-130 is approved, its significance is especially confusing; and especially important to understand.
First off, let's repeat that an approved I-130 gives a person no rights to remain in the United States. If you have a valid immigration status (for example, are within the time permitted to remain under a student, visitor, or other visa), you can remain until your permitted stay ends. But in any other circumstance, staying in the U.S. unlawfully while awaiting your green card is likely to result in that green card being denied rather than granted. See Must You Leave The U.S. to Wait For Your Green Card?
The issue is that U.S. immigration law penalizes people who stay in the U.S. unlawfully. Those who remain unlawfully for six months or more and then leave voluntarily will face a three-year bar on returning. Those who remain unlawfully for a year or more and then leave voluntarily face a ten-year bar on returning. For details, see Understanding the Three and Ten-Year Bars for Unlawful Presence.
Foreign nationals who are deported (removed) from the U.S. could face an even longer bar on returning, depending on the reason for their removal. The bottom line is that the U.S. immigration authorities want people to wait for an immigrant visa OUTSIDE the United States.
Notable exceptions exist, however. For example, immediate relatives of U.S. citizens can actually file their I-130 along with an application for adjustment of status (the main form for which is the I-485), upon which their U.S. stay becomes lawful. They will be given a work permit while they await their green card interview.
And a few other categories of people are also eligible to adjust status in the U.S.; meaning they wouldn't have to leave for a consular interview, and therefore wouldn't face any bar on returning.
As you are no doubt noticing, this is a highly complex area of immigration law. Any questions about your own case, in particular your eligibility to adjust status, and whether you would face a time bar if you applied for your green card via a U.S. consulate, should be directed to an experienced U.S. immigration attorney.