There are two general categories through which one may obtain lawful permanent residency through a family member, Immediate Relatives and Family-Sponsored. The differences between these two categories are significant. Immediate Relatives, or the parents, spouse, or unmarried and under 21 year-old child of a United States Citizen, are not subject to a visa waitlist. However, those who qualify for a Family-Sponsored visa could be subject to a long wait depending on the annual numerical limitation. Please remember that a foreign national has no right to visit the United States during the prolonged wait for a visa.
The five categories of people who qualify for a Family-Sponsored visa are listed below.
A cutoff date for processing is updated monthly at the Visa Bulletin:
https://travel.state.gov/content/travel/en/legal/visa-law0/visa-bulletin.html
First preference — Unmarried, adult son or daughter of a U.S. citizen
Second preference (A) — Spouse or child of lawful permanent resident
Second preference (B) — Unmarried adult son or daughter of permanent resident
Third preference — Married, adult son or daughter of U.S. citizen
Fourth preference — Sibling of a U.S. citizen