LiveUSB

Making a USB key of Fedora

You are probably looking for this document, which tells you step-by-step how to create a Live USB key of Fedora using a pre-existing ISO file you downloaded from somewhere (probably spins.fedoraproject.org or get.fedoraproject.org):

https://fedoraproject.org/wiki/How_to_create_and_use_Live_USB

Making your own custom USB IMAGE of Fedora

You may be interested in creating your own custom ISO from scratch. If so, you'll want to read this page:

https://fedoraproject.org/wiki/How_to_create_and_use_a_Live_CD

Some documentation on kickstart might be handy too:

https://fedoraproject.org/wiki/Anaconda/Kickstart

Good luck!