Under the folder 'first_app' there are a list of R files. These are a mix of files which pertain to the exercises in the Mastering-RShiny book, and files which I have gone on to develop as templates that may be useful. Typically these templates expand on the work of the book.
Under the folder 'webinargolem' there is a blank golem template, following along with https://shinydevseries.com/post/golem-demo/. Note this has nothing to do with the 'first_app' files. It's just another tool for advanced Shiny.
insertUI_case_study is an example of adding UI elements from a module into a main app. Akin to https://shiny.rstudio.com/articles/dynamic-ui.html