Countless eons of evolution of life — and later the evolution of the mammalian brain – came long before anything resembling a word.
As the members of the human species evolved to the next phase of their development, they became language-users. At some point in their development, humans found it useful (maybe necessary for survival) to communicate. Certain grunts, yelps, signals, etc. came to signify something: a warning, a request, a threat.