>>Controls are like Containers, with the difference that all its objects are hidden. This is very useful if you build "Containers" which functionality should be totally hidden. Thus when you use these controls on your form, you don't see its members.
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>Can somebody give some examples?

I use very often a control in which I drop a textbox to display a Path, and a button with which the user can locate a path (using the GETDIR() command).
These two objects (textbox + button) work always together, having only one of them, doesn't make any sense.
This control can have many functions built in, via methods in the controls PEM's. You can drop this control on any container/form, and you can use it to let the user choose a path and display it.

Using a control in this case is hiding complexity. You would do this for the same reason as you would hide or protect methods or properties of objects.
You will make less mistakes by using them, and you will keep a better overview in your containers/forms.

Christian