Learn the first 100 most commonly used signs in American Sign Language (ASL). But, that's not enough? Learn the second 100 most used signs. And so on. But, don't forget grammar. See 'Learn ASL' for tutorials in grammar, sentence structure, culture, etc.
The word list is subject to change over time. It doesn't have to be exactly 100, but it can be a bit more or less 100.
Variations: there may be regional/generational variations of some ASL words across the regions of North America. And contextual variations.
Inflections: most ASL words in the dictionary are "fixed", but many of them are grammatically inflectable within ASL sentences.
Meanings (semantics): These "fixed" ASL words in the dictionary may not mean the same in different contexts and/or ASL sentences.
ASL is very much alive and variably constructable as any spoken language. The best way to use ASL right is to immerse in daily interaction with Deaf/Ameslan people (ASLers).
First 100 words.
As you feel more comfortable with the first few hundreds of ASL signs, progress further with your vocabulary and learn signing more.