Shortly after arriving on the scene in Metropolis, Superman saved a runaway train from terrorists. Something someone said made him remember his father showing him the rocket he arrived on. Clark began looking at old microfiche trying to find record of a comet, etc. that could have been him.
The Daily Planet exploded after hearing of a new costumed hero in Gotham City. Superman went after this "Batman," not knowing if he was friend or foe. Batman was taking down Magpie, who'd ripped off jewels and killed several. After almost ruining the catch, Superman left Batman and returned home. On the news, he heard of a new Black Canary, and of a satellite falling from orbit. He headed to Coast City to stop it. Green Lantern was already on it. Together, they were able to stop it from crashing.
While visiting his family, Clark learned of some freak weather that was happening nearby. Superman encountered the Weather Wizard and the Flash for the first time. Working with the Flash, they stopped the Weather Wizard. As with Batman and GL, Superman inquired as to how Flash got his powers.
Another weather situation was occurring, and Superman found Aquaman trapped under a tree in a hurricane. He freed him and headed into the storm, though Aquaman warned him not to. Poseidon knocked him unconscious and hurled him into the sea. Aquaman saved him and they headed off into the desert to wait out the god's wrath.
At a Denver fire, Superman encountered J'onn Jonzz, a Martian shape-shifter. Not long after, the Justice League formed. The Daily Planet got word that they were all fighting each other, and Superman headed out to investigate. He found a giant robot, which was creating illusions. He destroyed it, and the operator disappeared. They took him to their headquarters and offered him membership. Still unsure of where he came from and how he got his powers, Superman declined.
Seven years later, Superman received an apparition of Jor-El, his Kryptonian father. The vision told him of his heritage.