Icons:
An icon directly represents an idea, concept, or action. Icons make it easier to work with a graphical representation for the user.
Icons are commonly used in applications to represent what the application is used for and a key element of the UI / UX interface.
Logos:
Logo is used to recognize the main part of the symbol used to represent the organization. His way of representing the organization can be direct or covert. The logo must be associated with the organization. This reflects on the thinking of the organization and presents a graphical summary of the organization.