How did Frege distinguish an expression’s sense from its referent?

In the philosophy of language, Gottlob Frege distinguished between an expression’s referent (Bedeutung) and its sense (Sinn) to explain how different expressions can refer to the same object while providing different information.12

• Referent (Bedeutung): This is the actual object or entity in the world to which an expression refers. For example, the expressions "the Morning Star" and "the Evening Star" both have the same referent: the planet Venus.132
• Sense (Sinn): This is the "mode of presentation" of the referent. It represents the way in which the referent is presented to the mind. Because different expressions can present the same object in different ways, they possess different senses.12

Frege used this distinction to resolve the puzzle of informative identity statements. While the statement "Everest is Everest" is trivial, the statement "Everest is Chomolungma" can be informative because, although both names share the same referent, they provide different senses—or different ways of identifying the mountain—thereby making distinct contributions to the thought expressed by the sentence.1