The Rapport skill is all about making positive connections to people and eliciting positive emotion. It’s the skill of being liked and trusted.
Use Rapport to charm or inspire people to do what you want, or to establish a good connection with them. Charm your way past the guard, convince someone to take you into their confidence, or become the man of the hour at the local tavern. For nameless NPCs, this is just an overcome action, but you may have to enter a contest to sufficiently ingratiate yourself to a named NPC or PC.
Create an Advantage
Use Rapport to establish a positive mood on a target or in a scene or to get someone to confide in you out of a genuine sense of trust. You could pep talk someone into having Elevated Confidence, or stir a crowd into a Joyful Fervor, or simply make someone Talkative or Helpful.
Rapport doesn’t cause harm, so you don’t use it for attacks.
Rapport defends against any skill used to damage your reputation, sour a mood you’ve created, or make you look bad in front of other people. It does not, however, defend against mental attacks. That requires Will.