when i can apply uscitizen after getting greencard?

Answer 1

If you are interested in applying for U.S. citizenship, first make sure that all of the following apply to you:

you have lived in the United States as a lawful permanent resident for at least five years (with exceptions; for example, the time period changes to four years if you got your green card through an application for political asylum, and to three years if you got your green card through marriage to a U.S. citizen and you are still married to and living with the citizen. There are other exceptions for refugees and U.S. military personnel.)
you have been physically present in the United States for at least half of the last five years
you have lived in the district or state where you are filing your application for at least three months
you have not spent more than a year outside the United States
you have not made your primary home in another country
you are at least 18 years old
you have good moral character
you are able to speak, read, and write in English
you are able to pass a test covering U.S. history and government, and
you are willing to swear that you believe in the principles of the U.S. Constitution and will be loyal to the United States.

Answer 2

The basic rule is 5 years and 3 years, but you can actually file slightly earlier:

You can file your application 4 years and 9 months after the issuance of your green card.

If you received your green card through marriage to a US citizen (and you are still married to that person), you can file 2 years and 9 months after the issuance of your green card.

Answer 3

you need wait 5 years to apply for U.S citizenship
or wait for 3 years due to marriage