There are multiple ways to get a green card as a relative of a U.S. citizen. As the spouse, unmarried child, or parent of an adult citizen (over 21 years old) you qualify as an immediate relative. Green cards for immediate relatives are unlimited, so there is no waiting for a visa as an immediate family member. Receiving a green card will allow you to live and work in the U.S. as a permanent resident.
If you are already in the United States, to receive a green card, you will file need to file for permanent residence. Second, you will petition for your status as an immediate relative of a citizen. For immediate relatives of U.S., these two steps can be done at the same time or you can submit your petition and then file for residence.
If you are not yet living in the U.S., you must submit your petition for residence as a family member of a citizen first. After your petition is submitted, there is a waiting period for a visa to allow you to travel to the U.S. This process is the same for immediate and non-immediate family members of citizens.
Remember to keep in mind that your status as a child will most likely be counted from the date of your petition, and that to keep the status of child you must be 21 years old or younger. Also, children under 21 must be unmarried through the green card process in order to count as immediate relatives. If you are the married child of a U.S. citizen you do not count as an immediate relative, but can still petition for residence as a family member of a U.S. citizen.