Captain America's real name is Steve Rogers. He is a fictional character created by Joe Simon and Jack Kirby, first appearing in Captain America Comics #1 in March 1941.
Steve Rogers was a scrawny, asthmatic kid from Brooklyn who was rejected from military service during World War II. A secret government program called Operation: Rebirth gave him an experimental super-soldier serum, which transformed him into a peak human specimen with enhanced strength, endurance, and reflexes. He was given a vibranium shield and became America's symbol of hope during the war.
In the Marvel Cinematic Universe films (starting with Captain America: The First Avenger in 2011), Steve Rogers is portrayed by actor Chris Evans. The character has been central to the MCU's Avengers storyline, spanning from World War II through to modern times in the films.
Pro tip: If you are asking because you are getting into Marvel films or comics, start with Captain America: The First Avenger for the origin story, then move to The Winter Soldier (widely considered the best Cap film) and the Avengers ensemble movies.