Your Webhook will contain the logic to validate the user input and assess whether that input is OK or not. Your Webhooks will thus be used in one or more T-Dialogs in one or more slots. A content editor typically selects the script from a drop-down, yet you as a developer can register them yourself and set them in the T-Dialog where needed. The scope of your role allows you to access the T-Dialogs editor.
NOTE: the evaluation of the slots are in parallel, not one after the other.