Sometimes you might want to just test out and OS without the hassle of setting up another partition or wasting valuable hard rive space. A live USB is a good way to solve that problem. Note this tutorial will work with almost all linux distros it does not have to be ubuntu. I just like ubuntu.
By Max Ballard
Step 1: Download the ISO From Ubuntu Website.
go here and download whatever version you want: http://www.ubuntu.com/download/desktop
I recommend 64 bit if you use more than 4 gb because you wont be able to use more than 4 with 32 bit. I also recommend getting 14.04 LTS instead of an experimental version if your new to linux. (LTS means long term support)
Step 2: Download Universal Installer/ Unebootin.
Go to here for universal installer: http://www.pendrivelinux.com/universal-usb-install...
Go here for unebootin: http://unetbootin.github.io/
Step 3: Install Onto Usb.
Run your installer program(unebootin/ universal installer) and select Ubuntu. select Go to where it says select your ISO. Browse through your drives to wherever you downloaded the ISO from the first step, and select it.
Step 4: Running Ubuntu.
Restart your computer. Press f11 when the bios flashes and select your usb drive. It should show up as a cd/ dvd along with its name. Also if your running windows 8 be sure "secure boot" is off. Then you should get a screen asking you if you want to install ubuntu or just run it one time. Be careful if you decide to install it, that your data on the drive is backed up.