First thing to do is to format the USB stick with Gparted. If you want to format from the command line do like so:
And find the name of your USB stick. It could be something like sdb1, sdc1 or whatever. But firstly be sure about what is your device.
Then you can format your USB stick with a FAT16 or FAT32 filesystem:
Where sdxx is the name of your USB device. If you want to create a linux filesystem:
Now to make the newly created partition bootable type:
press the key "a"
press the key "q" to exit from fdisk
Now you have to install syslinux on the USB stick. For doing this go to the syslinux web site http://www.syslinux.org/wiki/index.php/Download and download the latest version.
Now you have to unpackage syslinux and cd into the directory syslinux/linux
Here open a terminal and type:
./syslinux -i /dev/sdxx
this command creates the file ldlinux.sys in /dev/sdxx
Then with a text editor create a file named syslinux.cfg and write this in the file:
Then copy the files vmlinuz and initrd.gz onto the USB stick in the / directory. These files can be found in the .ISO image of your distribution.
Well done! you have now a bootable USB stick.