Provided you're a US citizen and you want to sponsor your parents for a green card, first, you need to submit an I-130, which is a form that confirms you are related to the person you are sponsoring. You will also be required to submit your birth certificate and other biographical data on you and your parents. Once your family-based petition is approved, you need to figure out if your parent needs a waiver. If they have any criminal or immigration violations, they may need one of these. They may qualify for a waiver of forgiveness if you or your siblings served in the military, they entered the US with a visa, they have TPS or DACA, or if they came to the US a long time ago and someone has already tried to apply for a green card for them. Finally, after the Family Petition is approved and you've decided whether your parents need a waiver of forgiveness, you must submit the completed application to the appropriate embassy, which may or may not be in your parent's home country.