What is Root? What can it do? Where can I get it for an android tablet 5.1 lollipop version without a virus or anything? Is it worth doing a root?

Root is a hack for android devices that allows you to unlock your devices full capabilities. It's allows you to acces your devices main files, and you can delete preinstalled firmware. Certain things require root to run, but personally I would avoid rooting due to it voiding your contract with the provider company.