Thanks to this guy (Rob Barron), I now understand Depth of Field and Aperture.
Depth of Field - http://www.youtube.com/watch?v=BfOC_Msb1dI
Aperture - http://www.youtube.com/watch?v=xG7CmMepYHw
This is a two part video about Lens
Part one - http://www.youtube.com/watch?v=VGAUIBSLJhI
Part two - http://www.youtube.com/watch?v=DTVZ4gfs_mg
Depth of Field - http://www.youtube.com/watch?v=BfOC_Msb1dI
Aperture - http://www.youtube.com/watch?v=xG7CmMepYHw
This is a two part video about Lens
Part one - http://www.youtube.com/watch?v=VGAUIBSLJhI
Part two - http://www.youtube.com/watch?v=DTVZ4gfs_mg