How to put .iso file to USB? [duplicate]
You can also try UNetBootin which should install the .iso and everything up for you.
(Although like the previous answer, your other files will be wiped)
The simplest way to create a Linux install disk (on USB) is to use the 'Startup Disk Creator" application.
Just click on Dash icon (top left), and type startup (then click on icon).
Note: This will overwrite (and erase) any files already on the USB drive. You should use a spare USB stick of 2GB or 4GB capacity.