video playing on its own page

I have a problem with video I’m using the “Presentation Demo” Gallery 2 I have some videos and they are playing at very small size (4 columns) in the page. How can I make them come out big when you click on them and maybe open on its own page. I want these videos to play as big as possible once you click on them and I need to have a description under each video.
I can’t find any information on how to do this
Thanks for your help