Welcome.
Chapter 4 of Vincent Moret's book is devoted (47 pages) to a tutorial on the Grand Prix Attack...it's an excellent, instructively presented introduction....
Use the "Look Inside" feature (located just above the book's cover graphic) on this webpage to view the table of contents of the book. - then scroll down to p.55 for an excerpt from the chapter on the GPA...
https://www.amazon.com/First-Chess-Opening-Repertoire-White/dp/9056916335/ref=sr_1_1?crid=NIPUDDFFAOPH&keywords=my+first+chess+opening+repertoire+for+white&qid=1564950849&s=gateway&sprefix=my+first+chess+op%2Caps%2C191&sr=8-1
Thanks RussBell and kindaspongey for further info!