American Sign Language is a beautiful language, with its own grammar and rules. It has handshapes, manual markers, classifiers,and movement. It is similar to spoken language having intonation,rhyme, rhythm and pace. When people sign in American Sign Language, the intent of the message can be understood by the actual sign (I am hungry... I am not hungry)or by classifiers or facial expressions. You can sign "I am not hungry" by using the sign "not". You can also sign "I am not hungry" by signing "I am hungry",but using your eyebrows in a negative way and shaking your head 'no'.
In addition to signs, body movement and classifiers, you can finger spell. There actually is a sign language called The Rochester Method,where everything is fingerspelled. I am not talking about this. I am talking about some words don't have a sign "car" or "job"...Kids very young can see the letters b-u-s and see the handshape rather than bus and learn that those movements mean a bus.
As children grow older, I think it is vital that more fingerspelling occur. An interpreter, teacher, parent or friend might sign a sign "energetic" but the real word was " enthusiastic". It helps the deaf child or person if you then spell the word. It is important that the deaf person understands the word in English,too,because s/he might see it later and now can associate it with a sign. This is not done for every word,but rather for some signs that have multiple meanings. Fingerspelling helps the deaf or hard of hearing person learn English words, learn spelling and helps clarify vocabulary. It is essential to do this as new words are learned, so that the learner can become familiar with new vocabulary.