If you need to export a group of contacts, you can use Lists of Filters to select groups fo contacts:
From the Audience tab, navigate to Import and Export > Export Contacts
Choose 'Start New Export'
Choose the Filter or List you want to use to select your contacts (or choose 'ALL')
Choose the fields you wish to include - its important to note that by default, all fields are selected - if you don't change this to just the fields you require could result in very large file sizes
Click the Export button, and monitor progress:
You can download the report at any time - it will remain available until deleted.