Question about Device callbacks

Hi!

I'm a newbie using MDX Framwork to learn MDX and have a question about Device object callbacks. When exactly are they called and are there some general rules what to do in which callback (i.e. where to load effect or texture from the file)
I.e. in "DirectX Managed" docs there's:
"Framwork.DeviceReset Event
Occurs when the Microsoft Direct3D Device object is reset."

It doesn't really explain when the Device object is reset.
I'm interested in the following Framework callbacks:
OnCreateDevice
OnResetDevice
OnLostDevice
OnDestroyDevice.

Thanks in advance

Game Technologies: DirectX, XNA, XACT, etc.8

I've found info about these callbacks in DirectX SDK examples.