Short answers, pulled from the story.
Character creation defines a player character before any story begins to unfold. It records physical, mental, psychological, and social attributes using specific game mechanics alongside informal descriptions of appearance or personal back-story.
Rolling four six-sided dice and adding the highest three generates ability scores between 3 and 18 in some Dungeons & Dragons editions. Some Dungeons & Dragons editions offer an optional point buy method for determining ability scores instead of random rolls.
The Stormbringer role playing game used a single die roll of 100 sides to determine both race and class. Players have little control over scores generated this way but gain diversity among new characters.
Sometimes the game master decides the outcome before the player even touches their dice. This initial step belongs exclusively to the player rather than the gamemaster who runs the session.
Traveller models a character's life prior to becoming an active adventurer through career cycles. Empire of the Petal Throne uses similar methods to build history before gameplay begins.