Describing your character gives you the opportunity to bring them to life, by giving your adventurer its physical description and a personality. Here you also give your character their backstory, telling of their life before becoming an adventurer, their ideal, bonds and flaws.
Below you can find some examples of Ideals/Bonds/Flaws from D&D sourcebooks to get you thinking.
Personality Traits
Ideals
Bonds
Flaws