How did language developed? What makes words what they are?

It is my understanding that language is just a collection of sounds that make sense to a certain community and that new words/expressions develop by people developing 'filler' expressions (in accordance with their language) for ideas and items they are then unfamiliar with. Various 'fillers' can be developed at various times, just for one item/idea, until eventually one or more of the 'fillers' just so happens to stick and become part of the people's lexicon; effectively, a new word.