The Brawl skill covers all forms of unarmed (or unconventionally armed) close-quarters and short range combat. For using melee weapons, see Battle. For using ranged weapons, see Shoot.
Overcome: Since you don’t really use Brawl outside of a conflict, it’s not often used to overcome obstacles. You might use it to display your fighting prowess in a demonstration, or to participate in some kind of regulated bout or sport fighting, which would allow you to use this skill in a contest.
Create an Advantage: You’ll probably use Brawl for many of the advantages you create in a physical conflict. Any number of special moves can be covered with advantages: a targeted strike to stun, a “dirty move,” disarming, and so on. You could even use Brawl to assess another fighter’s style, spotting weaknesses in his or her form that you can exploit.
Attack: Brawl is all about Attacking. You make a wide variety of physical attacks with Brawl, unarmed melee, unconventionally armed melee (with, say, a broken bottle as a weapon), and thrown object attacks. Remember, this is for relatively close-in work, so you have to be in the same area as your opponent. Thrown objects have limited range.
Defend: You use Brawl to defend against any other attack or create an advantage attempt made with Brawl or Battle, as well as pretty much any action where violently interposing yourself could prevent it from happening. You can’t use this skill to defend against Shoot attacks, unless you're picking up an unconventional shield.