As for installing and adjusting a new derailleur. I find it very simple - easier (to me) than installing a front derailleur. I recommend using the derailleur's instructions for this, maybe a video to make it clearer if it isn't. The diagrams are usually very clear. There's plenty of videos online. Bolting it on is simple. Then you just adjust the high and low limits, which are very simple and objective settings. Then the cable and indexing. All of this - as well as chain length - are pretty simple and will be in the instructions and many online videos and other sources. If you have any specific questions for the installation and adjustment, just post a new thread here.

Other than possibly a chain tool (only needed if your spare links are too long), there's really no special tools needed. Hex key (aka Allen wrench) multi tool and regular, small screw driver if you don't already have those.