What does it mean to get a green card after being married to an American citizen for ten years?

You apply for marriage immigration after you marry an American citizen.

If you pass, you will get a green card, which is a "conditional green card" with a term of two years.

You can't divorce in these two years, otherwise, your green card will be invalid.

You will be deported at any time.

Time is up. You're not divorced. You are qualified.

Your spouse should sign the letter from the immigration office.

You can turn it into a formal green card.

The term of a formal green card is ten years.

In the meantime, if you don't want to take the naturalization test, or you don't take the naturalization test.

Then in ten years, your green card can be renewed.