It looks kind of hard. How much playing experience do I need to start using the book?

You should be able to play the common barre chords comfortably and be able to name them.

You should be ok with starting to learn about spelling scales, and learning the terminology of harmony (it is easy).

You should consider removing all your pedals from your signal chain so you can hear your guitar “straight” when practicing. It will be easier to hear squeaky or weak notes.

You should accept that your left hand fourth finger is going to be used as a strong independent finger in soloing.

I’d recommend you listen to some classic improvisations in the styles you like. I consider John Mayall and the blues breakers with Eric Clapton to be a master class in rock and blues soloing. Immerse yourself in that record when you get the chance.

If you’ve had lessons, learned modes, or have experience playing solo’s I’d ask that you take the time to fit what you know into the fingering system here, and keep an open mind for simpler explanations.