I have seen in some books that an "s" is used in their conjugation. For example "vous est partis". But isn't it the case that "vous" refers to a singular noun ? What should i write in the exam if the teacher simply wants me to list out the conjugation of verb, the one with 's' or without 's'?
When the past participle requires an agreement, this agreement should follow the logic, i.e. agree with the person(s) is applies to. It is only guessable without context when il/elle/ils/elles are used.
Je suis parti / partie
Tu es parti / partie
Il est parti
Elle est partie
On est parti / partie / partis / parties
Nous sommes (parti / partie)1 / partis / parties
Vous êtes parti / partie / partis / parties
Ils sont partis
Elles sont parties
1 Very rare
No, all that is quite wrong; the only possibility in the plural is this:
vous êtes partis.
Use a conjugation site, much information will be given you when you need it; there are several but here is a good one: Le Monde.
For the agreement when "vous" is the so called "vous de politesse" (only one person) there is no agreement (no s, see this).
vous êtes parti