Welcome,
https://www.nysdot.gov/main/business-center/contractors/construction-division/construction-repository/PMRefMan.pdf
Not sure if it is the manual for the version you have but seems like Primavera as well as many software vendors are making available their manual in PDF to anyone as this is a download from a government site.
There is a well known book titled CPM in Construction Management, by O'Bien and Plotnick., used by many fans of Primavera products. I do not use it as I am not any longer a fan of any Primavera product, therefore from my viewpoint it is irrelevant, but not necessarily from yours, in such case look for it. I don't believe this book will disclose the mathematical errors in P6 and the limitations for shift modeling as well as the lack of more advanced resource modeling that are missing in P6.
Eventually if you dare to explore beyond the limits of P6 you will discover what many like NASA with Stottler Henke's Aurora has, that the resource leveling capabilities are not so good. Just look at the following reference.
http://www.stottlerhenke.com/products/aurora/Turnaround/2009-10-01_Aurora_WhitePaper_Turnaround.pdf
Well I compared my choice, Spider Project to P6 and Aurora and got even better results. Let me know latter-on when you feel comfortable with resource leveling so we can compare some resource leveling results.
Here we dare to debate such issues in the hope the scheduling community will benefit from sharing the knowledge.
If you have no problem with WBS then you are having a good start as many at the beginning have problems with it.
In my opinion this is the best place to learn about scheduling, you will be surprised of the diversity of themes, from logic to claims, there is even a trivia section.
Best regards,
Rafael