There are three basic types of visual components.
Components do not have a design time render other than a component place holder. Components do not have an x, y positioning. Examples include TIWTimer.
Controls render themselves with a placeholder at design time. Examples include TIWEdit, TIWGrid, TIWLabel, etc.
Containers contain other components. Examples include the form itself, and regions.
Components support a variety of capabilities. Capabilites are not exclusive, and are often combined.
All components must support the ability to render. That is, output HTML and/or Javascript.
Many components are render only. Examples of render only components are TIWLabel and TIWMemo.
Submit components can be used to send data back to the server. Examples include links and buttons.
Input components return a value. Examples include TIWEdit, TIWListbox, and TIWCheckbox.