As a verb:
* "The artist was flattered by the museum's offer to purchase her painting."
* "He tried to flatter the boss by praising her leadership skills."
* "The compliments about her new haircut were flattering."
As an adjective:
* "She wore a flattering shade of red that brought out the color in her eyes."
* "The lighting in the restaurant was flattering, making everyone look their best."
* "He gave a flattering speech about his colleagues' contributions to the project."
As a noun (less common):
* "The politician's flattery towards the voters was transparent." (This usage is often used in the context of insincere praise.)
The specific usage of "flatter" depends on the context of the sentence and the intended meaning.