Here is a quick look at the first four films, that were made in the 70s and 80s.

Superman (1978) - The original film sees Christopher Reeve play Superman.
With the planet Krypton facing destruction, scientist Jor-El takes drastic measures to preserve the Kryptonian race - he sends his infant son Kal-El to Earth to become a champion of truth and justice. Kal-El grows up as Clark Kent and eventually learns the truth about his family and realises that he must use his abilities for good. Clark moves to Metropolis where he becomes a mild-mannered reporter for the Daily Planet newspaper, and also becomes his alter-ego, Superman, a defender of law and order. However, deep below Metropolis Lex Luthor is plotting evil. Can Superman thwart his nasty plans and save millions of innocent people?

Superman II (1980) - Christopher Reeve returns - The adventure continues.
Superman saves France by throwing a nuclear bomb deep into space. Unfortunately the bomb explodes, freeing three Kryptonian criminals from captivity. Meanwhile Superman has decided to relinquish his superhero powers to live happily ever after with Lois Lane. As the criminals, led by General Zod, join up with Lex Luthor to take over the world, Clark Kent has to decide whether to try to regain Superman’s powers and face his biggest battle yet.

Superman III (1983) – If the world's most powerful computer can control even Superman...no one on earth is safe.
Superman has saved the world against villains from Earth and from Krypton, but will he cope when a super-computer, and its programmer, set out to destroy him? In between his attempts to save the world, Clark returns to his old High School and meets an old flame.

Superman IV: The Quest for Peace (1987) - Nuclear Power. In the best hands, it is dangerous. In the hands of Lex Luthor, it is pure evil. This is Superman's greatest battle. And it is for all of us.
In an attempt to take over the world arms market Lex Luthor clones Superman to make Nuclear Man. Luthor hopes Nuclear Man will take on and beat Superman. Thankfully, Superman saves the Statue of Liberty, repulses a volcanic eruption of Mount Etna, and rebuilds the demolished Great Wall of China. And saved the world.