Contact lists can be imported from external sources as a .csv file. 

To Import Contacts from the Main Menu click Contacts.

On the top left of the Contacts page click Import Contacts. 

After clicking Import Contacts a pop up should appear.

NOTE:  To insure that the Contacts are imported successfully downloading the sample file is highly recommended. Also the column headers are to be identical and the uploaded file needs to be .csv format

The file should look similar to this:

Once the .csv file is ready click Upload File, select the .csv file and click Open.

After clicking Open, another pop up confirming that the upload was successful should appear. That confirmation is the final step in importing your contacts.