I'm new to rooting (and Android) too, and one of the main reasons for wanting to root is that I can update my firmware without having to wait for HTC to release it in my region or carriers to release it to users. I can just wait for a ROM based on that update and then just use that ROM.
Rooting also opens up some options that you otherwise can't change. Like I was able to make the volume button work as shutter, make the app drawer transparent, disable blinkfeed, and a few other things.
By my understanding, by rooting your phone, you're basically giving yourself full access to the system and you're free to make any changes you want. Obviously, this comes with risks.
I think I started out by asking around about which ROMs are good, and then following instructions on the xda-developers.com website.
http://forum.xda-developers.com/forumdisplay.php?f=2115#romList (looks like it's temporarily under maintenance though).