[Gambas-user] Concept of containers

[M. Cs.]

I don't understand the concept of containers. When I want to create a UI
which would proportionally change its size (e.g. when I double the size of
the form, every item doubles its size), do I have to cover all the area of
form with panels or vboxes (what's this?), and then to place the real stuff
(buttons, labels, views etc.) inside them?
What is the use of containers? Could someone explain me the concept?