If you are currently running Ubuntu yourself all you need to is go to
Startup Disk Creator and the relevant ISO for Ubuntu. Couldn't be
easier really :-)

Then all your friend needs to do is boot from the USB drive and many
systems have a key to hit during boot to select the boot device. F12
is the most common but I've seen F9 and F10 used for this. Might need
a trip into BIOS to enable it too.