Historic means "important," "momentous," or "historically significant."
Historical means "relating to the past."
Examples:
- "America has entered one of its periods of historic madness, but this is the worst I can remember." (John Le Carre)
- "The Sixties are now considered a historical period, just like the Roman Empire." (Dave Barry)
- Yesterday there was a historic event in Spain: the coronation of King Felipe VI.
The event has historical significance because Felipe has become king while his father is still alive.