The example in comments only shows you how the function might be called, it's not how it would be defined. In particular, the parameters in a definition are never enclosed in quotes.
Then, the purpose of the function is not to return a random number. The random number will be used as an index to select an item in the argument, and that is what will be returned. So if you pass a word as the argument, what the function would return could be any single letter taken out of the word.