What is a database?
A database is where an app keeps anything it needs to remember between visits: customers, bookings, orders, messages. Without one, everything resets the moment somebody closes the page. It is the difference between a poster and a working shop.
Almost anything that feels like a real application needs one, which is why it is the point where a lot of projects stall. Setting one up traditionally means choosing a provider, creating it, connecting it and keeping the connection secret, and any of those four is enough to stop somebody who does not write code.
In Ura, asking for the thing is the whole process. If what you describe needs somewhere to remember, the database is created and connected for you, and you never see a connection string.
Does every app need a database?
No. A site that only shows information, like a portfolio or a brochure, does not need one and is cheaper and simpler without it. You need one the moment the app has to remember something a visitor did.