Every Story has a beginning. Your background reveals where you came from, how you became an adventurer, and your sense of your place in the world, drawn from experiences of your own and of those around you.
Choosing a background provides you with important story cues about your character’s identity. The most important question to ask about your background is Why Things Changed, though the question that most people will want to know if they are wise is What Changed?.
Character Development
The PHB has a section on developing out your character starting on page 121. The XGE has a section on developing out your character starting on page 61. Excepting notes about appearance, these sections are made strong use of.