The first thing I would like to mention before getting into the meat of the Cache API is that this subsystem is one of the best documented ones (at the time of writing). You can check out the main entry page (https://www.drupal.org/docs/8/api/cache-api/cache-api), and I recommend keeping it close by when carrying out Drupal 8 development.
The Cache system in Drupal 8 provides the API needed to handle the creation, storage, and invalidation of cached data. From a storage perspective, it is extensible, allowing us to write our own custom cache backends (CacheBackendInterface). By default, however, cache data gets stored in the database and hence the default backend is DatabaseBackend. Going forward, we will focus only on this implementation, ...
