As a U.S. citizen or green card holder, you're free to marry a foreign national or non-citizen immigrant - but you'll need to consider immigration laws to move your new spouse to the U.S. permanently.
You can't lawfully stay in the U.S. just because your I-130 petition was approved. It's only the beginning of a long process to become a permanent legal resident.
Becoming a citizen is open only to certain people, most of whom have already held a U.S. green card, learned English, and can meet various other criteria.