In order to Cure a disease, you have to accumulate 5 cards of a single color in one character's hand (4 if that character is the Scientist), and travel to a Research Station. Once there, you will have the action option to "Cure" on that character's turn.
I recommend playing with the Researcher and Scientist because on the first turn, everyone starts in Atlanta together and the Researcher can give a card to the Scientist to help get you closer to curing a disease.