Rooting for those of you that dont know, means giving yourself root permissions on your phone. It’s similar running programs as administrators in window, or running a command with sudo in linux.
With a rooted phone, you can run apps that require access to certain system settings, as well as flash custom ROMs to your phone, which add all sorts of extra features,
Is Rooting Illegal?
No. technically, it’s once was, but exceptions to the DCMA have made it legal for most phones (but not necessarily tablets).
Either way, it’s hard to imagine anyone actually enforcing this rule (much like DVDs for your own personal use).
Can I Unroot my phone?
Yes. If you decide you don’t like being rooted, you can often find instructions on unrooting your phone as well.
Usually it involves flashing as RUU, SBF, or something similar to return the phone to truly stock settings.