The partitioning wizard will scan your computer's hard drive and offer possible solutions for installing Linux-Mandrake based on the disk's contents.
The easiest solution is to erase the entire disk which will destroy everything on a drive.
Another option is to "Use free space on the Windows partition". This will automatically shrink the FAT partition to make room for Linux, but is only for when Windows occupies one large partition that spans the entire disk.
"Use existing partition" is for manually assigning Linux mount points when multiple partitions already exist as seen on the next page.