that a device you want to use needs to be formatted with any kind of filesystem should be clear indeed ...
the important part is that the device needs to be *partitioned* ...
some windows applications format usb keys directly without creating a partition table, if your device shows up as /dev/sda instead of /dev/sdaX (where X is a number) in the output of dmesg after plugging it in, then it has no partition table. i would recommend using something like gparted to partition and format such an usb key.
that a device you want to use needs to be formatted with any kind of filesystem should be clear indeed ...
the important part is that the device needs to be *partitioned* ...
some windows applications format usb keys directly without creating a partition table, if your device shows up as /dev/sda instead of /dev/sdaX (where X is a number) in the output of dmesg after plugging it in, then it has no partition table. i would recommend using something like gparted to partition and format such an usb key.