Please enquire well in advance (2 to 3 months) at the Swiss Embassy or Consulate in your country to find out whether a visa is necessary or not.
The secretarial office of the Cours de vacances can produce an attestation de préinscription (pre-enrolment attestation, without any mention of the payment if you haven't paid yet) or an attestation d'inscription (enrolment attestation, with mention of the amount paid). It may help you in the process of getting your visa but the Cours de vacances cannot intervene otherwise for students.
If you are coming to Switzerland to study for one term or more, you can ask the Admissions Department directly : www.unil.ch/immat.
Click on the following link to have direct access to the information for obtaining the visa (more than 3 months stay).