When you have been around the industry for a little while, you will see that nearly all applications, especially user-facing ones, are made of only three kinds of things: Forms, Reports and Workflows. A Form is simply an interface, a screen or a page, for the user to input some data. It is made of text fields, checkboxes, drop-down menus, and so on. A good Form offers prompting and validation, such as a text field that is supposed to be a number is actually a number and within a sensible range. It can be dynamic, updating fields depending on each other, all sorts of fancy things, and when the user is done, saves the results in a database.
A Report is a screen or page that accesses a database, often one populated at least in part by Form input, filters, sorts and aggregates the records, and presents them in a useful way, for example a graph or a table. Often Reports have a few Form-like elements too, so the user can refine or drill down into the data. A Workflow simply links Forms and Reports together. Behind both you might have Services (APIs). So 4 things, to make (nearly!) any application you can think of.
Let’s consider a website like Amazon. You go to it, and it runs the default Report. You refine that Report into a selection of things you’re interested in, and select one, fill in a Form to buy it, and the database is updated, one item transferred atomically from their inventory to your basket, by calling a Service. Then in the warehouse someone runs a Report that tells them what to pack and who to ship to, then they fill in the Form to update the status. There’s nothing in this, fundamentally, that couldn’t have been done on a 1971 IBM 3270, it just might not look as pretty to modern eyes, but all the functionality and interactivity would be there. If you’re buying a book, do you really need a photo of the picture on the cover to decide?