Most of my computers don´t even have a cd/dvd player anymore. It is like when the floppy disappeared. But the world will move on. You can not just download a Debian iso and put it on a USB stick. We need to make it bootable from our computer.
First step is of course to download a Debian image. I usually use the small net install image. But you can make any of the Debian images bootable.
Second step is to download and start UNetBootin. You will find it at source forge. Check out this link to UNetBootin.
Just to keep it neat and clean I format (Fat32) the USB drive before making it bootable.
Start UNetBootin and select Diskimage, and select the Debian Image. Make sure you have selected the right drive and click OK.
The process should only take a few minutes and that is all it takes. Your USB drive is now read to boot up a new Debian computer.
Happy booting!