The Brawl Market is the in-game shop for everything related to Brawl (and Gauntlet). You may access the Brawl Market from the Brawl menu.

The Brawl Market has two parts: the Limited Market and the Token Market. You may switch between them by using the tabs on the top of the screen.
 
The Token Market allows you to buy Token Packs of varying rarities which yield tokens for several different dragons. You may also purchase single Tokens for specific dragons. The dragons featured change every 24 hours and there is a limit to how many Tokens you can buy for each dragon per day, indicated by a red banner. The fewer tokens are available, the more the price will increase. 
 
The Limited Market allows you to use Brawl Medals earned from the Brawl Pass to purchase Token Packs, Card Packs, as well as individual dragons. Different dragons are featured every season.