You can view more examples with the videos below
http://www.youtube.com/watch?v=eFY5MQlrF_Y
http://www.youtube.com/watch?v=UN54rR4T4MQ
http://www.youtube.com/watch?v=gvdl4XdeNDI
http://www.youtube.com/watch?v=7YOZA2EFcKs
Additional notes at the link below
http://www.sparknotes.com/math/calcab/introductiontointegrals/section1.rhtml