How to Create a Multiboot USB-Stick

You need:

-http://www.pendrivelinux.com/yumi-multiboot-usb-creator/
-a bootable USB-Stick

First execute YUMI and click I Agree.

Then you can select your USB-Stick. Be sure you select the right one.

If your USB-Stick isn't formated in the FAT32 filesystem click format.

Next step select your image of the your Distribution.
If you don't have a image you can also download it by clicking "Download the ISO"

Now you can click "Create" and the Files get written to your USB-Stick.

The only thing you have to do anymore is to enable the USB-Boot in the BIOS.