The story of Oedipus is a tragedy in a few different ways. The first and greatest tragedy is the one of Oedipus attempting to avoid his fate. When he heard of the prophecy saying he was going to kill his father and marry his mother, Oedipus ran away. He was so horrified by this prophecy that he tried to escape this reality, but he ended up running right into it.
Oedipus unknowingly kills his own father when thinking he is killing the passengers of a carriage that attempted to run him off the road. Oedipus kills his father, but it is said that King Laius was killed by a group of robbers, not one man, so Oedipus believes he is in the clear. But in fact, the woman he thought was his mother was not, and the man he thought was not his father was.
In a very confused and twisted story, the prophecy comes true and Oedipus blinds himself out of horrification.