Let's start with this: you will want the Safestrap bootstrapper/recovery to install ROMs and keep your stock experience untouched, in case something gets messed up.
Two things to note: Safestrap creates virtual copies of some of the partitions used by your phone and mounts those rather than the actual partitions used by stock. In order to do this, it creates something called slots in internal storage on the phone. Each slot carves out about 2-3 GB of storage, depending on how large you make the /data partition of the slot. Knowing this, it's probably a good idea if you are using Safestrap to use an external SD card and change the camera app to store photos on external SD rather than internal storage. If you need help with that, just say so.
Anyway, to install Safestrap, you need to allow third party installs in settings->applications. Download the latest Safestrap (3.05, I believe) from the site of the developer of Safestrap, Hashcode, which you'll find here: Goo.im Downloads - Browsing safestrap
Put that on internal storage or external SD on your phone. Use a file manager app to navigate to where it is stored (there is an app called Files I think that will do this.) Tap on the .apk file; it will prompt you to install it, and let it go ahead.
Run Safestrap. Tap the button that says install recovery. At some point the SU app will ask you to allow superuser access to the Safestrap app. After recovery is installed, restart the phone.
If you see the very obvious Safestrap start screen, prompting you to press menu to start recovery or search to continue booting, then Safestrap is installed. Go ahead and press search and start the phone and I'll let you know what to do next.