The GED is a high school equivalency diploma and it is valid for entry into NY State (SUNY) and NY City (CUNY) Community Colleges.

The NY State Education Department site has various resources listed by county in NYC and NYS:
New York State GED Site
Frequently Asked Questions
Testing Sites and Dates by County

The NYC Department of Education has additional and resources listed for NYC residents.
Other Ways to Graduate
NYC FAQ
Full and Part Time GED Programs in NYC