What dual monitoring consists of is having two monitors linked up to your computer. It is easy to set up, you need obviously two screens, you plug them both in your computer and then have to change a few settings in the computer preferences to be able to have your desktip displayed on both monitors. You can setup more than 2 screens for your computer, but this requires an additional program and additional entry ports. Both can be bought but are often only required for specific needs. So dual monitoring is already quite good.
Now why would you want to have two monitors ? Well, first of all you desktop space will be doubled. Therefore you can have more icons on your desktop without being over flooded. Secondly it is great for multitasking. You can open two seperate programs at once an work on both at the same time. You open each software on a different monitor that way you can switch easily from on to an other. This is great for example if you are writing a document. You can look up information on the internet on one monitor, then leave the page open, and use the other monitor to write your resume or text. This avoids having to switch between the two, which you would have to do if you only had one screen.
However the desktop tool bar cannot be extended to the additional screen. It will always stay fixed to main monitor. This is a windows setting and you cannot change it, unless you buy an additional microsoftware. But this realy isn’t necessary. So basically using two monitors will help you work better, and view more at once. If you are using a laptop, it enables you to have a bigger screen as main monitor, since the laptop screens are often quite small.