But I don't know how to make the stick bootable, nor do I know where the fdisk program is.
You should be able to choose your boot source by tapping one of the function keys while BIOS is loading. Mine is F12.
Can't you just go into your BIOS settings when the puter powers on? You can change your boot sequence (priority of sources). Lots of BIOS have delete as the button to load. So just keep clicking delete after booting/rebooting and the BIOS should load up. Then make your external drive the top on the boot sequence list.
Why even use fdisk? You want to partition? Make your swap, boot, root, home files or whatever? It's all in the GUI after you boot, so you shouldn't have to use the command prompt.
The Ubuntu forum is fairly helpful, I've wandered around there a bit.