Contacts can be added one by one, contacts can be pasted into a form or a file with contacts (Excel, CSV or text) can be uploaded on the "Add/Import Contacts" page in your account.
Step by step instructions to export data from Outlook, Outlook Express, Yahoo, etc. to a CSV file you can upload to your account are included.

To store contacts data, an unlimited number of fields and groups can be created.
Screen Shot:  adding one contact at a time
Screen Shot:  uploading a file with contacts