For default use of the TFA module using the SMS Framework follow these steps.
* Install SMS Framework module and choose an available gateway
* Install TFA module
* Add a user field for storing a user's phone number
* Visit Administration > Configuration > People > Two-factor Authentication to choose the user field for use
Optionally you can allow certain user roles to skip the TFA process by giving the 'Skip TFA process' permission at Administration > People > Permissions.
Note, if no field is enabled or populated for a user the TFA process will not be started.
API:
Consult tfa.api.php for directions on extending TFA with different channels and storage.