Clinton didn't lie, exactly, which is part of the problem. He tried lawyering his way out on a technicality.
Essentially: Starr asked 'you fucking her?' and Clinton answered 'not fucking, no.'
He asked for clear definitions, for which he was roundly mocked, and he gave some answers that might pass muster in a court of law. Unfortunately his trial was a big dumb show by much worse philanderers. Also unfortunately, he did in fact sexually exploit an intern half his age.