As a noun:
* The detective found a clue in the dusty attic, a faded photograph with a strange inscription.
* The crossword puzzle was so difficult, I couldn't find a single clue to help me solve it.
* The missing child left behind a clue - a half-eaten apple near the playground.
As a verb:
* The detective tried to clue the witness in on the details of the case.
* The teacher clued us in on what to expect on the final exam.
* The author clued the readers into the mystery by revealing the secret in the last chapter.
In a phrase:
* Not a single clue was found at the crime scene.
* She was completely lost, with not a clue as to where she was.
* The detective was clueless about the motive behind the crime.
Choose the example that best suits the context you have in mind!