If you are not already familiar with the term, an Extrovert is someone who thrives on the energy that comes from being around other people. Especially when it is lots of other people.
These characters will typically enjoy being the face of the adventuring party and may even do most of the talking for the party. You can almost picture them like vampires (Strahd or Dracula, for instance) feeding off the energy of others. But regardless of them wanting to be out front most of the time, they can certainly have their moments of quiet alone time as well.
An Introvert, on the other hand, is one who regains their energy from being alone or being around as few people as possible. These characters will usually prefer the quiet moments in their room after a big battle or maybe the intimate moments conversing with a close member of their party in the rare instances of peace after defeating a BBEG.
Imagine Obi-Wan Kenobi or Yoda (Star Wars) spending a couple of decades being mostly alone on planets at the far reaches of the galaxy. But even though they typically prefer their alone time, when moments strike them some introverts will readily seize the spotlight and even relish being the center of attention.
Regardless of whether your character is an Extrovert or an Introvert, make sure to give them both moments in the spotlight and moments curling up with a quiet book. Even if those moments aren't in equal quantities. Only you will know what those moments will be and when to roleplay them within your game's storyline.
And from one introvert to another, have fun reading books about killing extroverts . . . er, um . . . Strahd.
- Writer exits room while laughing vampirically.