How to make bootable usb stick

Have an old USB drive lying around that you don't use anymore? Turn it into an operating install disk for Windows, Linux or Mac, or a diagnostic tool for your PC. A common use of a bootable USB flash drive is to use it for booting into Windows. This can allow you to perform diagnostics on a computer that has hardware issues or can't boot into Windows. You can also use the flash drive to install Windows, instead of using the Windows installation CD. Follow this guide to learn how.
first of all just downloads small utility "Rufus" from internet.
Rufus is an utility that helps format and create bootable USB flash drives, such as USB keys/pendrives, memory sticks, etc.

It can be especially useful for cases where:

you need to create USB installation media from bootable ISOs (Windows, Linux, UEFI, etc.)
you need to work on a system that doesn't have an OS installed
you need to flash a BIOS or other firmware from DOS
you want to run a low-level utility

Despite its small size, Rufus provides everything you need!
       DOWNLOADS rufus 

How to use Rufus 1.2.0.183: Step one

You can download Rufus directly  website.  Once downloaded, you can run it directly - no installation is required.

How to use Rufus 1.2.0.183: Step Two

Make sure you know where your .iso file located and insert the USB flash drive you plan to use. Copy off any files you want to keep as Rufus 1.2.0.183 will format the drive before copying new files on.

How to use Rufus 1.2.0.183: Step three

Ensure that Rufus is set to the correct drive and is outputting in the right format. The key things to look out for are Device and Cluster Size. All you need to do here is make sure that is going to output the .iso file onto the correct USB stick. The default cluster size will be fine, so leave it set to 32Kb.

How to use Rufus 1.2.0.183: Step four

Ensure that the Create a bootable disk using: option is checked, otherwise your laptop or PC won't be able to boot from the USB drive.

How to use Rufus 1.2.0.183: Step five

Rufus will start working automatically and there should be nothing more you need to do until it has completed. We used a 600MB .iso file and it took less than five minutes to process, so you can see that Rufus is no slouch.

How to use Rufus 1.2.0.183: Step six

Once Rufus has finished, simply eject your USB stick and put it into the computer you wish to install the .iso file on. Reboot or power up the computer and it should boot from the drive. If not, enter the BIOS and ensure that 'USB drive' or similar is set to be the first or primary boot device.