During a conversation, I want to output different responses according to different user inputs. What should I do?

There are several ways to do it.

Solution 1: Branching a dialog flow, and add a condition in each branch. The condition could be whether a slot value is null. Please refer to Bot Reply Conditions.

Solution 2: Calling Webhook. The response is dynamically generated by the value retrieved by calling webhook. For example, query the balance of an account.