If you want to create a Ubuntu Live USB or if you want to install Ubuntu from a USB drive, most instructions will tell you to use the Startup Disk Creator. I thought that Startup Disk Creator used to come with Ubtuntu, but just a minute ago when I tried to find it on a fresh Ubuntu 20.04 install it wasn't there.

Luckily, all that you have to do to install the Startup Disk Creator on Ubuntu is to run:

sudo install usb-creator-gtk

Or if you're using Kubuntu, run:

sudo install usb-creator-kde

That's all you have to do and then you can find Startup Disk Creator from the main menu.