The presence of an unreliable narrator means that the reader doubts the credibility of the author.
Unreliable narrators are almost always first-person narrators. Sometimes, the author's incredibility is seen from the very beginning of his work, he may be making a statement that is known to be untruth or a claim that is beyond reasoning. He may also state that he is mentally ill or impaired thus not able to tell a story correctly and accurately. At times, the falsehood of the described story is not revealed till the very end, the reader discovers some facts that prove the story void or incorrect. It would be a twisting ending that would make the reader reconsider his point of view of the story he had just read.
Sometimes, the author's unreliability is never fully revealed leaving the reader wondering about the intent and purpose of the story.
