If you have become engaged, congratulations! You likely have many things to plan for the big day. If either you or your fiancé or fiancée is an American citizen, however, you may need to plan for immigrant as well as a wedding. If one partner is a US citizen and one partner is not, there are a number of immigration forms that need to be filed to ensure that the couple can live together in the US.
As a couple, you will generally need to file Form I-130 (Petition for Alien Relative). This form is filed by the US citizen and can secure an immigrant visa for the spouse. You can file this immigration form after the marriage in order to sponsor your new spouse. The application form can ensure that your spouse gets a green card through marriage, so that your new spouse can live and work permanently in the US.
If you are not yet married, you will want to apply for a K visa if you plan on getting married in the US. The K visa will allow you to travel to the US for the purpose of marriage. While it is a non-immigrant visa, it does allow the non-US citizen in the relationship to adjust their status after the marriage is official. To apply for a K visa, you will need to file the Petition for Alien Relative (Form 1-130) and a Petition for Alien Fiancé(e) (Form I-129F). These immigration forms ensure that the wedding can take place in the US and ensure that your new spouse can get a conditional green card after the ceremony. After you have been married two years, your spouse will be able to apply for a permanent (non-conditional) green card through marriage by applying for adjustment of status.
Whether you are already married or only engaged, US law allows you to sponsor your new spouse if you are a US citizen. The exact immigration forms you need for your marriage will depend on how and where you get married. If you are already married or are married outside of the US, you will need to sponsor your spouse after the fact. This may mean that you and your spouse will need to remain outside of the US until a green card can be secured. If you are engaged, you can choose to apply for a K visa and get married in the US. The benefit of this is that your spouse will be able to travel and live with you in the US with no delay. You will be able to secure a green card soon after you are married.