Outlets are different units within the same location.
For example, you could have a location where you have an á la carte restaurant and a bar. Instead of creating two merchants, you create two outlets.

To create and outlet, select a merchant, click on Outlets and click Create New



You need to add products to the outlet in order to sell them.
The guide on how to do it is here:
Adding Available Products To An Outlet
If your outlet has table service, you need to create tables for that outlet. The guide on how to do it is here: