Your customers are the soul of your business. Knowing them and their shopping habits, keeping track of their purchases, and nurturing your relationship with them can make or break your business. Any information from a customer that is relevant to your business constitutes your customer database. The kind of information you have in that database depends on the nature and specific needs of your business.
How do you create a database? There is numerous CRM software available that captures the relevant information such as buying choices and patterns, or you can choose the bootstrap method and use a simple excel spreadsheet.