Many PCs (desktops, laptops, netbooks) don't have a DVD Drive, which means that it is difficult to install an OS. In contrast with Linux distros, where you can make a bootable USB stick easily, in Windows is not so simple. But there is a program that can make things better.
You need
The iso file of the OS you want (32/64bit). I tested it on a Windows 10 (Technical Preview ISO).
A USB Stick (at least 4GB, the more the better).
ZOTAC WinUSB Maker
How to
Run ZOTAC WinUSB Maker (is portable, no installation needed) and drag 'n drop the USB icon (from "My Computer") into the program's window. When finish, do the same and for the iso file.
That's it. Now click on "Make USB Bootable" and wait for the program to finish. When done, USB will be ready for use. Boot your PC from USB and install the OS.