Words as features of a neural networks
You need to make a dictionary of words. It means you have to make a dictionary which you assign each word a unique value. then you can use one-hot-encoding to represent each word uniquely. If this is what you need it will do what you want. But this has a big problem. When you think about cats and dogs, you may find similarities and differences between them. This is because you have more knowledge than the only representation of words in your brain. Consequently, you should use approaches to assign a unique number to each word, and put near concepts as neighbors. For the first part take a look at here and the second part, take a look at here.