About the BIOS in the instructions are not written.
1 Download Win32DiskImager
2 Download an image file from the download section
3 Unzip Win32DiskImager-0.9.5-binary.zip and run Win32DiskImager.exe
4 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.
5 Insert a usb key or a sdcard on your computer
6 Select the image and the drive in Win32DiskImager.exe like on the following screenshot and click on Write
7 Once finished, go on your usb key/sdcard and check that it looks like this
Playstation for PC (x86_64) In the table (Supported Systems (by architecture)) Indicated (Working)