OK we need to start from the beginning...
This is not a bells and whistles beginners book and if you're starting out on your own this book is not the one you want. That said, if you have a tutor (very highly recommended) and you want to take grades you have two choices (if you have an electric guitar) - and the following is my view only...
Rockschool system offer the possibility of learning 3 generic tunes, numerous scales, chords, ear tests etc and is the most popular system
RGT system offer no tunes, but you are expected to learn more scales (at higher speeds - at least at the early grades), more chords and more improvisation with those chords and scales but is otherwise similar to Rockschool.
Both will help you to become better and more rounded players.
I personally choose the RGT system because of the greater requirements for chords and scales etc and I think it provides a more 'musical' knowledge basis however, there is a lot to recommend Rockschool. Bear in mind if you choose RGT you can still choose to play the tunes you love in addition to your studies.
If you choose the RGT you need this book if you choose Rockschool you need their books. Either way neither Rockschool nor RGT books are a replacement for a teacher who will be of greatest help in becoming the guitarist you want to be.