The Free list is a list of users that you can call, chat and communicate with for free. Generally, these users are your friends and family for whom you don't want to charge for your time. Adding a user to your free list is pretty simple and let them connect with you for free.
Note that people that you already have in your phone contacts are automatically available for free as you already have their phone numbers. Correspondingly, the same applies to users that have your phone number. You can decide to remove any users from your free list at anytime.
Please remember that adding a user you wish to contact for free will first need the approval of the other party as they will need to accept to let you contact them for free. The same applies to you when someone wants to contact you for free.