I was curious too:

An immigrant who marries a U.S. citizen is generally eligible for a green card. But current federal law requires immigrants who entered the U.S. illegally to leave the country and re-enter legally to be eligible for a green card. Leaving the U.S. after living illegally in the country for certain periods of time can trigger a 10-year ban, leading many mixed-status families to not pursue this process.

The Biden administration’s policy would allow eligible immigrants to obtain a green card without having to leave the U.S. After 3 to 5 years of living in the U.S. as a green card holder, immigrants can apply for American citizenship.

Administration officials estimate that roughly 500,000 unauthorized immigrants with U.S. citizen spouses will qualify for the program. Applicants must have been legally married to their American citizen spouse by June 17. Those who are deemed to pose a threat to national security or public safety will not qualify.