After you’ve advanced through the main storyline of Save the World, you’ll get access to Daily Quests.
Daily Quests are pretty similar to the Daily Challenges that you can find in Battle Royale mode. Basically what you do is each day you’ll receive one Daily Quest that requires you do a particular task to complete. It can be killing X number of enemies with a certain type of hero or even completing X number of mission by a certain type of hero.
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Once you complete the quest, you’ll get a minimum of 50 V-Bucks, with only 3 Daily Quests offering more than that amount.
Similar to Daily Challenges, if you don’t complete the quest for that day, then another will be added the next day you log in with the max amount of three Daily Quests.
The third way you can earn V-Bucks is to complete the Storm Shield Missions.
If you don’t already know what they are, well, these are missions in each of the four areas that you unlock as you progress through the main storyline in Save the World. (it helps to understand the jargon that you don’t understand, just by trying out Save the World mode in your Fortnite).
Basically, each area has 6 Storm Shield Missions as you begin with it, and the remaining 4 unlocked ones are as Side Quests (I’ll get to this in a bit) which you will come across as you progress further into the game.