Hi! For the $10, you get the base game, The Dark Below, with all of the general rules for creating characters, rolling the dice, meeting challenges and playing the game. In Shades and Echoes, the supplement PDF, you get both some broad advice on how to structure different types of adventures through the Dark, as well as a collection of locations, threats and NPCs your players can encounter along the way. You're free to use those as-is, or tweak them to suit your game. Building your own challenges from scratch based on these examples as templates is fairly simple!
I hope that helps. :)