On the Contacts View list, select More. 

From the drop-down select Import.

Select an "Address Book" from the dropdown menu. This address book will be the one that you will import the contacts into.

If you are not importing contacts from a CSV file that you exported from another email client, select Custom.

Choose the character set. in most cases it will be Unicode UTF-8, but there are several other languages to choose from. Depending on your language/locale, choose the character set that best fits. 

Click Upload to locate the file that you want to import.

Note: the file should be in CSV format. This means that when you are saving a contact list in Microsoft Excel, you should save it as a ".CSV" file. 

Select Next.

Verify the information and select Next (fields are what you put in the columns and rows on your .CSV file such as first name, last name, email, etc.)

Next, you will map the fields with an "Address Book Field". Be sure to accurately select the fields that match those in your .CSV file. 

Finally, select Import. You will find your imported contacts in the Address Book you selected them to be imported into.