You play as either Bill or Lance after they were dropped off on some island off the coast of the United States to investigate an asteroid crash. Once you are dropped off, you have to shoot everything in sight to defeat the evil Red Falcon.
Contra was the first IDE scrolling shooter that allowed you to shoot in eight different directions. It was amazing at the time. You can shoot in midair, while doing over 5 backflips.
There were two sequels and one spinoff game after Contra.