The entrypoint to your application is the app/main.R file. It can load packages and other files with box::use(). You should not use ::, library() and source() calls in your code.
Each file should have two box::use() statements at the top (one for packages and one for modules). Avoid .... Sort entries alphabetically.
Each file in app/view should be a box + Shiny module. See app/main.R for example.