What are Web-apps
Web-apps or dynamic websites are applications that are hosted online. Web applications process the stored data to display after applying business logic to it. Privilege is also assigned so the information can be accessed by some users and not others.
Web application: Various components
Who can access what information on your web hosted application can be tricky. Authenticated goes farther than just holding username and password combination. It also holds information on who can access what parts of data, etc.
Database forms the core and the most important part of a web application. It holds information in the form of schemas, tables, JSON objects, etc. If the database can trigger events on it's own, then that makes an application real-time.
Cloud functions form the core staging area for business logic. Cloud functions can cater to triggers on the database or storage events. They can then implement logic on traditional events like sending a welcome email on account creation, etc.
Storage can imply a place where assets can be stored. These can then be accessed readily by various components of the web application. These can be pictures, music files, etc.
How your application is hosted isn't trivial. How 'far' the data has to 'travel' can be a consideration. Proper hosting may involve mirroring the server at various geographical locations and then syncing the data from time to time.