In Dialogflow ES, a webhook allows you to implement custom programming logic so that you can do things like read/write from databases etc.
In other words, it connects your chatbot (the user interface) to your backend (wherever your data resides).
For example, you can save your user input to an Airtable database by writing some webhook code.
You can create a webhook in the Fulfillment section. See how to create a simple Python webhook.
How to build your Dialogflow bot in under a week If it takes you more than a week to build the first version of your Dialogflow bot, then you are probably not following a good process. Here I describe some ideas on how you can speed up your bot development. This will be especially useful for you if you are not a programmer.