It’s funny,but I don’t think ubuntu’s installation instructions ubuntu’s installation instructions make this clear. The easiest way to install ubuntu from a USB stick is to download and burn the CD. Then, boot from it and claim you want to “try ubuntu”. All this, on a computer with a CD unit, of course.
Then, click the top-left button with the ubuntu logo in it to search for “startup disk creator”.
This is actually the same program as the one on the desktop named “Install ubuntu”,but the later assumes you want to install it onto your local disk, while the former automatically assumes you want to transfer the system onto a stick (if one is inserted). Wait about 15m and the system will be loaded and ready to be inserted in the computer you want.