It seems that places like www.pendrivelinux.com
are great sources to help the first time usb flash user.
There are basically four ways to make a usb.
Some specialized app that takes a live cd and puts it on a usb.
Same for choice two but the app is also able to add in persistence or casper file.
Three is a way to copy and ISO file to a usb and boot it that way.
Lastly is the ability of almost every common linux distro to install to a usb flash as if it were a real hard drive.
Each has it's use and weak points.