English courses for foreign people are called ESL (English as a second language). Courses can be held for day classes or night classes. Depending on previous experience and price, the classes may be for up to 8 hours 5 days a week or as little as an hour once a week. Many schools offer the opportunity to take a TOEFL tests to prove your competence at the end of the course.

If you already speak English fairly well, ESL courses are also offered in higher education institutions from community colleges to universities. Community colleges are much less expensive and will give very similar training. There are also classes offered at community centers that can be extremely inexpensive, but may be crowded and do enable you to earn a student visa.

Some of the best known language Centers:

Inluigua Language Center
551 Fifth Ave. 7th Floor
New York, NY 10176
(212) 683-8585
http://www.inlingua.com

Berlitz Language School
2 Rector Street
New York, NY 10176
(212) 766-2388
www.ny.berlitz.com

For a list of language centers in New York:
http://www.ny.com/academia/centers.html