The platform brush allows you to generate a grouping of tiles based on three algorithms: Noise, Noisey Cave and Random Walk.
Noisey will produce T-Block like platforms by randomly deciding how tall each column of your box selection will be.
Noisey Cave will fill your box selection with tiles and then take away the inside based on a Perlin Noise generator. This will produce cliff like or cave like platforms.
Edges Are Walls is a bool that allows you to determine if you want to include the border of your selection to the generation.
Random Walk method is based on the Random Walk Algorithm. This will produce similar T-block like platforms but with much longer sections of play space.
Clear will erase any tile on the target tile map set in the inspector. Think of it like a big selection eraser.