Hey there, Badass!
With the new XP Booster available in the Battleborn Marketplace, you may be wondering how to purchase/activate it. The purpose of this post is to walk you through this process.
Once you're in the game's Marketplace, head over to the "Misc." tab. Select the XP Boost (in this case, Double XP Booster).
Once you've purchased the Double XP Booster, it will activate immediately. This will be indicated by the timer shown next to your Gamertag/PSN ID/Steam ID and Platinum balance. The timer indicates how long your XP Boost is still active for.
You'll be able to see the results of your XP Booster in action when you complete a match or mission. When the game shows you how much XP and currency you've earned, you'll see the bonus from the XP Booster temporarily displayed.