Today we are going to create a Linux Bootable USB drive.
The first thing we need is a disk Image File.
An Image file is a file that contains a copy of a disk.
An ISO file is a CD-ROM Disc Image.
If you clone an ISO to a USB drive,
that USB drive will act like a CD Drive

Let's get a small Linux Distro called Slitaz
Slitaz is a version of Linux with a 
full Desktop UI (User Interface)
and it's only about 40MB

We are going to use wget to download the iso file.
wget is a command that will allow you to download
anything from a website as long as you have the URL 

Run this command (it is case sensitive):
 wget "https://tinyurl.com/slitazlinux" -O slitaz.iso

The '-O' (that's a capital letter O) 
will tell wget where to save the file

Now we need to find where our USB drive 
exists on our computer.
All Hardware devices should exists under /dev 
and USB Drives will normally start with /dev/sd 
sd standing for SCSI Disk
and it sill be followed by a letter a b c d etc 

So a simple way to look for your USB Drive is with 'ls'
(And it is VERY important to select the correct drive 
so you don't erase the wrong drive)
the 'ls' command will list files and directories for you.
so, before you plug in your USB drive 
(or unplug it if you need too)
run this command:
  ls /dev/sd* 

you may see a list of drives or you might see a 
"no matches found" message if you don't have any drives connected
Now plug in your USB Drive and run the command again:
  ls /dev/sd* 

Note which drives are listed that where not listed before.
For example you might now see /dev/sda 
You might also see /dev/sda1 and /dev/sda2 
Those are all the same drive,
the numbers are showing partitions on the drive.
We are not concerned with the partitions at this time.

We now know which drive is the USB drive.
We can now CLONE the ISO to the USB Drive.
We will use the 'dd' command 
You will need root permissions to do this.
If you are already root you can run the command 
other wise you need to use sudo before the dd command.

If your USB drive is /dev/sda then you will run this command
dd status=progress bs=4M if=slitaz.iso of=/dev/sda 
  dd if=slitaz.iso of=/dev/sda  

'dd' will not show any output while clone with this command.
Just be patient. 

this is what the dd command is doing.
if=slitaz.iso <-- 'if' is the input file (our ISO)
of=/dev/sda <-- 'of' is the output file (where we are coping too).

Once complete it's a good idea to run 'sync'
sync

You are done.
If all went well you just made a bootable Linux drive!