So already I've tried booting Ubuntu on a USB from the Mac's command line (verboes or something like that). But it didn't seem to work at all and said load size is too small or came up with a no entry symbol.
So I put a Ubuntu 32 bit on a CD and now I don't know how to boot it. I can't open up the boot menu as all of the important drivers are gone from the computer.
Best Answer
Mac hardware will always boot to an os chooser holding down option. You of course need a USB / thunderbolt / FireWire drive with bootable media at that point.
Newer Macs use internet recovery to net boot and from there you can repartition any drives and reinstall all drivers needed to boot macOS and start again.
For a PowerBook, you might also use cd / DVD media since internet recovery isn't an option for PPC hardware.