The first Secret Battle Star of Season 5 in Fortnite can be found just like last season. You unlock a new loading screen with a hint where the secret battle star is in the picture. But before you can unlock the loading screen and the secret battle star, you need to complete weekly challenge sheets. Since this is the start of the season you only need to complete the first 7 challenges.
Season 5 Week 1 Secret Battle Star Location
The loading screen you unlock for this challenge gives you the hint you need for the first secret battle star. The treasure map on the loading screen shows the free battle star in the umbrella shaped dirt pit west of Lazy Links.