I would say that you can probably begin just teaching yourself signs and some grammar online, but I definitely believe that you will eventually need a tutor or teacher. I believe this because, like any language, ASL has certain characteristics and things that can only be learned from a native/extremely good teacher. I recommend finding a teacher who is d/Deaf, hard of hearing, or very familiar with ASL and the Deaf community (most likely an interpreter). Additionally, if that person is someone from around where you live that is better because of there are some regional signs that vary from state to state.