Relationships between Components, Modules and Plugins in mvc

[eluser]Mahyar Ss[/eluser]
hi friends,

I'm confused!
in simple cms with CI how work Components, Modules and Plugins together!
(Technical relationship between these cases with MVC)

some cms use:
example: joomla

please explain their relationships in an application
With the mentioned technical reasons...

for example: i have saw com_poll in components also mod_poll modules
What is the difference?

i want to learn more about designing pattern and how do I use them for my program
(simple CMS with CI)

thnX!