If you test positive for an STI, treatment is free through the CeGIDD clinics. They can prescribe and provide the necessary antibiotics on site. If you tested positive through a private lab, you can take your results to a general practitioner (médecin traitant) who will write a prescription you can fulfill at a pharmacy.
Partner Notification
Notifying your recent partners is highly encouraged. France has excellent localized anonymous notification tools supported by major health organizations. You can use Préviens-Moi (previensmoi.fr), a tool launched by the NGO AIDES, or Notification Partenaire (notification-partenaire.fr), run by the French Society for the Fight Against AIDS (SFLS). Both services allow you to enter a partner's phone number to send a standard, anonymous SMS advising them that they have been exposed to an STI and should get tested, without revealing your identity.