Brawl Stage Studio is a PC stage builder for Nintendo's latest installment in the Smash series: Super Smash Brothers Brawl. It offers many new features not possible with Brawl's build-in Stage Builder like placing up to 252 blocks, loading custom stage preview images, having access to the beta block, placing spawn points and much more.
In order to load and play your stage in Brawl, you have to put the stage file into a specific folder on your SD card:
US : X:/private/wii/app/RSBE/st/ PAL: X:/private/wii/app/RSBP/st/ JAP: X:/private/wii/app/RSBJ/st/ (Replace 'X' with the drive letter of your SD card reader)