Rufus is an "online" tool used on Windows systems to help create bootable USB drives.
The system has been created to give people the opportunity to put pre-compiled images (ISO files) onto a USB drive, making it bootable. Freely distributed, it's mostly used to put systems into USB format, including the likes of Windows 10 and various Linux variants.
The point of the system revolves around the bootable feature. Bootable USB drives require an EFI "partition" to be created on the drive in order for the "boot" to be recognized by Windows. Simply copy/pasting the ISO file's contents onto the drive will not do this. This has made the use of a tool such as Rufus is often regarded as essential in the modern computing landscape.
The way the system works is by combining two important elements - the ability to write / copy the contents of ISO files onto a USB, and the ability to format the drive to suit. The formatting part is vital because it means that you're able to essentially put any type of data onto it (regardless of the source); the ability to write/copy files is important because it allows you to add files from any location.
When you load up Rufus, you have a number of options. The most important is that you're able to select an ISO (or some other content) that you wish to put onto the drive. The most important thing to realize with this is that there are a number of "pre baked" solutions you can use, one of which being "FreeDOS".
FreeDOS is essentially a clone of MSDOS that was distributed for free. In the absence of any bootable media for you to put onto a USB, you can use FreeDOS to perform disk utilities (such as fdisk) - a good set of computing utilities that not many people are familiar with. On top of this, you're able to specify which file system the drive uses as well as whether it uses "quick" formatting or not etc.
The reason this is important is because it gives you the ability to manage the various underlying ways in which you're able to manage different hardware components a system may have. This also means that you're able to identify any potential issues that could be preventing a system from booting.
I most recently downloaded a version of Windows 10 (1709) as an ISO. This was around 4GB, which was too big for any DVD's - meaning I had to put it onto a USB drive that had the required capacity. Without any native support for this in the Windows I was using, I had to turn to Rufus - and it worked extremely well.
By Richard Peck