I stand to be corrected if I am wrong, but my understanding is that
that information applies now to only old computers; all new Wintel and
WinAMD computers are now UEFI/GPT, rather than FAT/BIOS, and the
primary/logical partitions system, is obsolete for new computers, with
UEFI/GPT systems having up to 128 partitions, with no differentiation
between primary and extended and logical partitions.
Of course, I may be wrong, and, thence, stand to be corrected, if I am wrong.
I suggest (if you want to keep windows), to shrink the windows partition
with
gparted (there is a live dvd available), then install debian on the
unpartitioned space.