Im creating a broshure on the symptoms of cholera for a project and it says: create a public campaign to educate the masses of the illness. and i have no idea what that means.

A mass is a group of people. Basically, you want to educate a 'large group of people' about the illness that you are campaigning about. when it says educate the masses, it means educate society or the people that reside in the society as a whole, as a collective.

the masses are the people