I have many tutorials linked from the bottom of the googleAnalyticsR homepage, including Ryan's from above. You can also find a list of other Google Analytics -> R libraries if you don't like that one.
May I also direct you to the Dartistics website that I've published with Tim Wilson and others, which is aimed at digital analysts using R, and holds tutorials on using Google Analytics, Search Console, Adobe Analytics etc. data and applying various statistical methods to them, such as forecasting, regression etc.