Where can I learn sign launguage?

I’d like to relearn the sign language alphabet and most words in sign language. I think it’s very interesting and if I should ever meet someone who can’t speak and/or hear, I can easily cummunicate with them. However there is a small catch! I can’t really GO anywhere to learn, so it has to be online or something, and being only 14, I cannot afford it! So what I’d like to know, is if you guys know of any place where I can learn it for free online? Please let me know of any ideas or any suggestions, or possibly a book if it’s not too much money! Even if you think of a website, but your not sure if it’s free or whatever, please tell me anyways! I don’t know of ANY at all, and I won’t mind looking into your suggestions! Thank you guys SO much!
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