Customers or prospects are the organizations and companies you do business with and sell products or services to. They are normally imported from your CRM application such as Salesforce, either as part of the data upload for this application or during the proposal client assignment when a Salesforce opportunity is selected for a specific proposal.
You can list the customers from the "Master Data" menu by selecting the "Customers" sub-menu.

You will see a list of customers, which you can sort, filter and download to Excel.
Use the + button to create a new customer and x button to delete an existing customer.