When importing a Membership Benefit, the required fields are Benefit, Total Benefit Value and Unit Cost.  You can also add a Comment or indicate whether or not the Benefit has been sent. Our sample below shows all Default Values, but you can always use Source Fields as well.

The drop down for Benefits is linked to the Table of the same name in Configuration.  Comments are limited to 255 characters.
*If you would like to add all of the default benefits to the Membership mapping, use the option to do so in the Membership Area Settings.