En la página que pones hay un tutorial...
Installation Guide
Download*Etcher*for your OS
Download an image file from the*downloadsection
Install and run Etcher
Extract recalbox.img.gz (gz is like zip, ie it's a compressed file)
Warning : some browsers like Opera/Chrome/Safari take the liberty to unzip the file by themself and badly rename them. If the file is more than 1GB, it is already unzipped.
Insert a usb key or a sdcard on your computer
Select the image and the drive in Etcher like on the following screenshot and click on Flash!
[
http://batocera-linux]
Once finished, go on your usb key/sdcard and check that it looks like this :
[
http://batocera-linux]