What gives information to the cell?

The cells have antenna like molecules on outer surface called "receptor". Other molecules from body go and bind to the receptor. Those are called "inducers". Due to this, there is change in shape (scientifically called configuration) of receptor. This initiates a chain reaction type reactions inside cell that causes specific cell response.

Few molecules go directly into cell nucleus and cause gene manipulation.

Few examples of inducers are : Hormones, Cytokines etc.