He answered with one word. What do I do with that?

One word can acknowledge, agree, decline or leave a question unanswered. Its job depends on what came before it. “Okay” after a confirmed plan does different work from “okay” after a concern you wanted to discuss.

If the important point is still open, your next line can name that point. A brief reply does not require a longer performance from you, and it cannot establish a person's feelings on its own.