The tools palette displays the Visual Component Library, which has more than 100 components you can select and add to the form. Some components, however, are non-visual, meaning they don't appear at run time. The non-visual components expose functionality to the program you are creating, such as connecting it to an external data source. Once you drop a component onto a form, you can customize it with the Object Inspector, a two-tabbed window that displays the component's properties and events. Properties are characteristics like size and color.
Events are methods called by the component in response to given conditions.
Buttons have an OnClick event, for example. Double clicking on a particular event opens the code editor window where you can write the event handling code in Object Pascal. In Delphi, each form is its own class, and the components added to it become members of that class. You can also add your own fields and methods to the class's private, protected, or public sections. The form's graphical representation and its code are stored together in the Delphi project.