If you complete all challenges in Fortnite season 6 week 1 you can get the secret or hidden battle star. This star will give you 1 free tier.
You will only be able to obtain the star if you completed all week 1 challenges and if you have the battle pass.
Week 1 hidden star video
This video will show you the exact location of the week 1 secret battle star location of Fortnite season 6.
The star is located West of Paradise Palms. You will find a small hill, if you go to the South East of that hill you will find a red tractor. The hidden battle star is located on top of that tractor.