It is honestly very easy. I'd back up everything from your SD card to your computer, and from there, go into Settings, Apps, and enable USB debugging. Then power down your phone, pull the battery out and write down the serial number of your phone (I think there are a couple lines...you want the one that starts with S/N or something like that. Turn your phone back on. Then go to this website
revolutionary.io
You'll need to download the revolutionary tool, the driver listed, and the superuser zip (the superuser will allow you to utilize root access apps). Connect your phone to your PC and leave it in "charge only" mode. Again, USB debugging should be enabled. Install the driver. After that, you are basically ready to run the revolutionary file and get rooted.
Following a youtube video is a good idea, just make sure it's for the Evo and uses the Revolutionary method. There are older root methods that don't work anymore.