Debian systems usually have hotplug installed by default and hotplug should autodetect your usb-stick and also automatically load the needed kernel module. If there doesn't appear to be /dev/sda1 in your system, you can pluck the usb-stick in and reboot the computer. After that you should be able to grep some info about your usb-stick from the boot messages (dmesg | grep usb).
I have formatted my usb-stick for fat32 filesystem that both Windows and Linux understand (although Linux calls it vfat). I have created a directory called /media/usbkey and added this line to /etc/fstab :
/dev/sda1 /media/usbkey vfat user,quiet,umask=0 0 0
After this I can mount my usb-stick by plugging it in at any time and executing the command "mount /media/usbkey" and the files in the usb-stick will show up in that directory.