Most software applications that store contact data provide a File Save As or Export as CSV function. Contact managers such as ACT!, email programs such as Yahoo!, and database programs such as Access, all provide a File export function.
Many companies store contact data within Excel workbooks, and Excel makes it easy to create or modify a CSV file. Most database applications, such as Access and Filemaker, as well as contact managers and CRM systems such as ACT! or SalesLogix, allow you to Save as or Export you contact data to a CSV file.
Consult the Help documentation for your application to learn more about exporting a CSV file. Within the Help search function, try typing the term "export" into the search box. Look for topics such as "export contacts," export addresses," or "CSV."