The "Customers" entity is for repeating purchases. It can move on its own stages of pipeline, like leads. The main difference between the customer and the lead is that the pipeline stages represent the time until the next purchase.
You can enable Customers in the settings / general settings section (this feature is available on the Advanced plan):
You can add a customer in the "Customers" section, or if you have leads with clients who will buy again (make periodic purchases), you can go to the Digital Pipeline in the “Leads” section and set up the action for creating a customer when the lead reaches a certain pipeline stage. Customers have their own card. You can add contacts and companies to it, as well as other catalogs.
There is a "Purchases" tab where you can see the purchase history. You can add a purchase by pressing the "Add purchase" button, here you can set the date, the price and a comment.
The Customers section has its own Digital Pipeline. Customers can use the standard features of the Digital Pipeline by clicking on "Setup Pipeline" on the upper right corner. There are the following features available: create a lead, add a to-do, send an email, Salesbot, API: send a webhook and others.