Summary
In summary, Drupal is what you make of it. You can simply download and build a site with Drupal 8 using just the core functionality, or you can extend the functionality using modules freely available in the community. Going further, you can develop your own modules and themes and make Drupal 8 the base for a complex e-commerce delivery system, if that's what you want to do. Like the LEGO analogy, the limitation is only your imagination and, maybe to some extent, your individual coding skills.
The remaining chapters in this book will take you step by step through the modules and functionality you get with a stock Drupal 8 installation without any community-contributed modules. This will show just how much you can already achieve before you have to think about extending Drupal, let alone coding.