Newbie needs help with session guitarist

I'll leave the detailed explanation of Kontakt vs Reactor vs all the other tools to some of the more knowledgeable people on the NI framework. But hopefully I can get your started with Session Guitar.

In your DAW, setup your Audio devices (ins/outs) and your MIDI input like you would for any other plugin.

You'll want to add Kontakt 7 as the VST3 in your DAW. There is no Session Guitarist VST2 or 3, it's designed to be played in either Komplete Kontrol or Kontakt.

Once Kontakt is open click Library, this isn't mandatory but makes browsing easier. Scroll down until you find your Session Guitarist library and click it once. On the right you will see different presets. The big thing to pay attention to is the difference between melody and non-melody versions. In a nutshell the melody versions will allow you to play single notes and chords. The non-melody versions are designed to play a wide variety of pre-set strum patterns. Once you found the preset you want, simply double click and it will load.

Depending on the version of Session Guitarist you have, the patterns can be adjusted by modifying the ending and other parameters.

Hope this helps!

Cheers