Lol, so "the guarantor" is only a "he"

jen', ask your school or university for the the details. It is strange that they didn't give any details before you were accepted. If they are not accredited for full time study by Swiss law, you have very little chances of getting an appartement.

Do you mean the guarantor will be somebody you know (family, friends, etc.) that will cover the loss for the regie in case, you will fail to pay your rent or destroy the place?

If so, what I had, was a signed letter from the person stating that he stands as a guarantor for me. A copy of their id was also added. Probably the regie would be happy if they could have an extract of the guarantor bank statement, a certificate of non-pursuit, three last salary slip or anything else able to make them confident.

Good luck, as this probably won't be the only hurdle in the way to your apartment...sadly.

You will need from him a letter admitting he is your guarantor, 3 last payment slips, contract if possible, attestation from the pursuit office. You will need the same for your self (except maybe the 3 payment slips ) but then you will need to show your pocket money can cover the rent.

Normaly the guarantee is a deposit at a bank that is held in the name of the rental agency, incase of damage, unpaid costs/rent, of like an amout of 3months rent. 

Or you get SwissCaution, where you pay a small monthly payment and they guarantee the rental.

Clarify if that is what they are asking.

Or do they need someone to sign that they will take on any charges/responsibility that are caused by you, should you leave the country? 

This is what EPFL suggests/explains to students

This is a more detailed explanation about what is needed from the guarantor (in French)

Hope that helps!