The US immigration rule describes many narrow categories of individuals who could become entitled to a green card and you would require fitting in one of those to apply for.
If you are engaged to marry a citizen of the US, then you might get entitled for K-1 fiancé visa that would let you visit the US for getting married. And after your marriage, you could apply for adjust status.
If your parents, husband or wife, or kids over 21 years of age are citizen of the US, and your age is below 21 years, then you are called as their immediate relative and you might be entitled to a green card after going through the process of application, and your relatives who are US citizens are willing to file a petition for you and also pledge you economic support.
if your parents, your brothers, and sisters are citizens of the US and if you are married and your age is above 21 years then you are called as preference relative and you might get entitled for green card whenever visas are available in your category and if your relatives who are US citizens willing to file a petition for you and had promised to support you financially.
If you got an offer of a job from a US employer then you might get eligible for green card, if you got right qualification and background. if your sponsor is willing to sponsor you and some jobs might qualify you for provisional job visas like H-1B, that lets you do the job in the US for many years.
If you got around $1 million or over that for investing in making or expanding of a business in the US, then you might get eligible for a green card based on investment.
if you are a graduate from overseas medical school who had visited the US earlier also and still residing in the US then you might get eligible for a green card as a special immigrant.
if you are former foreign US government employee or retired employee of a foreign company who had worked for minimum half of the previous seven years in the US, then you might be eligible for a green card as a special immigrant.