This is where you would import the email addresses from email clients.You can import your contact list that can be exported directly from Outlook or Thunderbird. Or simply upload a generic CSV file with two columns : names and contact emails.
1.) Put Your  Name Here.

2.) Put Your Email Address Here

2.) Pick The CSV format to match your email client









3.) Put in the Name Of The CSV File You Exported

4.) Click "Import Contacts" and they will be brought int the system
What is a "CSV" File?
"A Comma separated values (CSV) file is used for the digital storage of data structured in a table of lists form, where each associated item (member) in a group is in association with others also separated by the commas of its set. Each line in the CSV file corresponds to a row in the table. Within a line, fields are separated by commas, each field belonging to one table column." ( from Wikipedia )
How to Export Contacts from Outlook
http://office.microsoft.com/en-us/outlook/HA011489021033.aspx

How to Export Contacts from the Mozilla Thunderbird or Netscape Address Book
http://kb.mozillazine.org/Importing_and_exporting_your_mail
Helpful Links
You Can Download A "Sample" CSV File By Clicking Here