The USA immigration allows several foreigners who have family members in the United States or are living with family members who are US citizens for quite a while and are lawful residents of this country to apply for a green card which is the permanent citizenship. If you are the spouse, a minor child or the parent of the US citizen, you need not worry about a long process for the immigration.
In the case, you are currently residing in the United States;you have to meet a few requirements in order to apply for your green card through family sponsorship
For close relatives, cousins and family friends, the procedure for applying through family sponsorship is completely different. Please talk to the immigration officer for details.