As one might expect, this reflects your character’s social skills such as persuading someone to help you, telling a little (or not-so-little) lie, or putting on a wonderful performance.
High Charisma characters are commonly portrayed as being charming and radiant people. However, a high Charisma ability is also important to a military commander who must use their presence and not necessarily their charm to command their forces. In either case, both rely heavily on confidence and carrying themselves in a way that people are more likely to listen to them.
A low Charisma character can be interesting to play. Their low Charisma score may stem from just being shy and having a difficult time relating to others. The character may have a distinct feature such as a scar or other wound that makes others unfairly avoid them.
Of course, it’s also possible that the character’s personality is just, shall we say, an acquired taste.