For very simple explanations... you can read this..
http://www.dpreview.com/learn/?/Glos...Balance_01.htm
then read this
http://camerahacks.com/2005/03/22/ge...t-filter-ever/
You can buy expensive discs that will do the same thing as the coffee filter..but I can get close enough with my cheap coffee filters and they fit all my lenses when I hold the filters in front of them
It also helps if you camera can do any kind of RAW mode shooting so you capture all the info and make your own fine tweaks later in the raw converter.