One of the privileges of being a U.S. citizen or green card holder (lawful permanent resident) is the ability to sponsor relatives to come live and work in the United States. As long as the relative isn't otherwise inadmissible, you can sponsor as many eligible relatives as you like. However, U.S. immigration law has a set list of preference categories, which affects which types of relatives will get a visa in a timely fashion.
Congratulations on becoming a naturalized citizen. One of the privileges of citizenship is the ability to bring your immediate relatives here to become lawful permanent residents, and possibly future citizens. Immediate relatives include any unmarried children you have who are under 21, your parents (if you are 21 or older) and your spouse. You can also sponsor your married children and, if you are 21 or older, your siblings.
You were a lawful permanent resident, but now you are a U.S. citizen. While you were a lawful permanent resident, did you file a petition to bring your spouse or children to the U.S.? If so, you may have been told that your petition was "family second preference." Family preference visas for lawful permanent residents are limited in number. If there are no more visas when the limit is reached, your family members will have to wait.