Want to learn more about ggformula? Here are some places to look.
TextbookRelated Resources
Several text books either use ggformula or have accompanying documentation that demonstrate how to use ggformula.

Foundations and Applications of Statistics: An Introduction Using R (R Pruim, second edition) is an Rinfused probability and mathematical statistics text that emphasizes connections between probability and statistics. The first edition of the book predates the ggformula
package, but the the second edition is supported by the fastR2
package and uses ggformula
for plotting.

Introduction to the Practice of Statistics in R (NJ Horton and BS Baumer) describes how to undertake analyses in R that are introduced as examples in Introduction to the Practice of Statistics, by David Moore, George McCabe, and Bruce Craig.

Statistics: Unlocking the Power of Data (Lock, Lock, Lock, Lock, and Lock) is an introductory statistics textbook that embraces a resampling approach.
An annotated companion to the examples in the book implemented using R can be found at
and the Lock5withR
R package provides all the data sets used in the text.

Stats: Data and Models (NJ Horton) describes how to undertake analyses in R for the examples in the Fourth Edition of Stats: Data and Models (2015), by Dick De Veaux, Paul Velleman, and Dave Bock.

Intro Stats (P Frenett and NJ Horton) describes how to undertake analyses in R for the examples in the Fifth Edition of Intro Stats (2013), by Dick De Veaux, Paul Velleman, and Dave Bock.

Open Intro Stats
OpenIntro Stats now has versions of their labs designed for use with the mosaic
package.
The mosaic
labs were adapted by Ben Baumer and Galen Long of Smith College and updated to ggformula
by Bonnie Lin and Nicholas Horton of Amherst College.