Many US citizens get married to citizens of foreign countries and they seek to bring those foreign national spouses to the United States and to do so they need to sponsor their spouses for US Green Cards. At the same time, they must also sponsor their spouses financially. Hence, the first thing that the US citizens need to do in order to sponsor their spouses for lawful status in America is to file immigration forms for them. If you are a US citizen who seeks to bring your foreign national spouse to the United States, you will have to file few immigration forms for her and that is the first step in the process of sponsoring your spouse for lawful status in America.
If your spouse is currently residing in the United States as a non-immigrant, you will have to file Form I-130, Petition for Alien Relative, for her and along with that, you must also file, Form G-325A, Biographic Information and Form I-864, Affidavit of Support and you need to submit two G-325A forms, for you and your spouse. As she is your immediate relative and as she can adjust her status to permanent resident status, she can file Form I-485, Application to Register Permanent Residence or to Adjust Status, concurrently while you file Form I-130 and she need not get back to her home country to apply for an immigrant visa. She can apply for adjustment of status and become a permanent resident, while in the United States.
If she is in her home town and if you are in the United States, you must file Form I-130, for her in the United States and you must also file Form G-325A and Form I-864. You will have to file Form I-864, in order to demonstrate that you will financially sponsor your spouse in the United States and to prove that she will not become a public charge. After the approval of Form I-130, your spouse will have to file an application for an immigrant visa in her home town and she can get into the United States as a permanent resident with that visa. Moreover, your spouse will never be put on a waiting list as immediate relatives need not wait until visa numbers become available.
While submitting Form I-130, you must also submit few other supporting documents such as a copy of your marriage certificate, copies of divorce decrees, death certificates, etc. You must also submit passport style photographs of you and your spouse. Apart from that, to prove that you are a US citizen, you will have to submit copies of your birth certificate (if you are a native US citizen), naturalization or citizenship certificates or your US passport.
If you are a Green Card holder and if you wish to sponsor your spouse for lawful status in the country, you will have to file Form I-130 for your spouse and your spouse who is in a foreign country will have to file an application for an immigrant visa after a visa number becomes available and get into the United States with that visa. Your spouse can adjust her status and become a lawful resident if she is in the United States while you file Form I-130, for her. In this case, she can file Form I-485 for adjustment of status after a visa number becomes available. While filing Form I-130, you must also submit, a copy of your Green Card, to prove that you are a lawful resident.