All Fortnite players obtain access to a group of free Starter challenges which enable it to unlock a small couple of rewards, though the weekly challenges and the greater part of unlockables are limited to Battle Pass owners. In addition to 10 weeks of challenges which will progressively unlock between Fortnite Items now and early July, the Battle Pass comes with new Blockbuster and Carbide challenges. Blockbuster involves completing all on the challenges in weekly and unlocks some as-of-yet unknown cosmetic reward. Carbide involves reaching different level milestones, with each offering some piece to upgrade the Carbide skin, along which has a pickaxe.
In regards to rewards tied directly to your Battle Pass, you will find more than 100. You could see a selection of skins above or have a look at everything available in this Season 4 rewards roundup. Again, as from the past, Epic estimates that unlocking everything will require between 75-150 hours of gameplay.
If you owned Season 3's Battle Pass, you'll gain five levels from the new Battle Pass automatically. Purchasing Season 4's will likely carry over a five level bonus into Buy Fortnite Items Season 5 once that begins. Those in a very hurry to level up may also purchase additional levels for V-Bucks.
Fortnite Season 4 runs through July 9, so provided you start out early, you should have just over two months for getting your hands on the many rewards. There's a lot of other new Season 4 content to look at, such as crashed meteor and updated map. For more, read throughout the Season 4 update patch notes.