To export a group of customers, or all customers - you can do so on the Customers page in Admin.
To export all your customers, click the checkbox next to the Name field. When the option appears, click on "Select all (X) customers".
Then, to export that list of selected customers - just click the "Export" (Download as CSV) button on the top right, and you'll get the option to choose the data fields (Name, Age, Date of Birth, Organization, etc) that you want the Export to include.
This will download your customer list as a CSV spreadsheet to your device.