What Site Can I Visit to Learn Sign Language for Free?

The short answer is "you can't."

Sign languages don't follow English grammar, so you can't just look up a sign in a dictionary and substitute it for English words. It is hard enough to learn a spoken language from tapes and books, but it's impossible to learn a sign language that way. You need to go to classes or get a tutor. Books and videos can supplement your learning, but you absolutely can not learn only from them. There are many important elements of signed languages that can't be recorded in print. Like "classifiers" which include a large amount of the adjectives and verbs.

If you want to just learn a few signs and call that sign language, you'd need to tell us which sign language you are wanting to "learn." I can only assume you are interested in ASL (American Sign Language) since there are more Americans on here than anyone else. There is no universal sign language.