Have you seen ANY of the Marvel movies?
To expound just a bit on what Zantera said, the basic background is: Since superheroes started coming on the scene, alien invaders (Avengers; Thor 2), fights with Hydra and other villains (Winter Soldier, Iron Man 3, Civil War), fights between superheroes themselves (Age of Ultron), and between superheroes and things they created (Age of Ultron) keep causing mass destruction and deaths of innocents. People are scared and want superheroes reined in. A U.N.-like body of governments led by the U.S. comes together and adopts a series of accords limiting superheroes' rights to function without government oversight and requires all "enhanced individuals" to be registered with the government.
Tony Stark (Iron Man), driving primarily by guilt over a lot of the problems he has caused, believes this is a good and necessary thing, and zealously backs the accords and the government. Captain America believes this is anti-freedom, and that there is something sinister behind it that needs to be uncovered. He also believes that, at times, threats are so great that there is a need to act immediately, and that wading through red tape will cause delays that will cost lives. The conflict is actually set up very well so that you can really see both sides of the argument. The "teams" are:
Pro-accords: Iron Man, War Machine, Black Widow, Black Panther, Vision, Spider Man
Anti-accords: Captain America, Hawkeye, Falcon, Winter Soldier, Ant Man, Scarlet Witch, Sharon Carter (sort of)