Help imac g3 relic and im a 14 year old but im qiute up on computers?

hi i got an imac g3 slot loader bondi blue 20 gb hdd and 256 mb ram i think its 333 mghz not sure well wen i got it it had running 10.3.9 and one day i turned it on and it was in os9 so i went to change the boot up system thing but it wouldnt restart and it started deleting random stuuf i now mac osx 10.3 is all there but its in another file and now wen i turn it on it that finder file that flashes to a ? then back so is it possible to install ubuntu like an old one if u could give me a link to downlad it would be grat i would also need very clear simple but detailed instructions i know this is a lot but please help as i love my mac also i will be doing every thing like downloading stuf on a laptop windows emachine d620 please aswell if i plug the ethernet in ma laptop and the mac can i select the boot file on ma laptop for the mac to boot from?? any help thanks remeber simple terms and trhat im doing it in windows computer thanks for any advice???