Confused about works cited, quoting, and sources, MLA style?

(using MLA style for my essay)

If I’m using someones data from a page and that page has the source, do I just put where I found the information or do I use the original source location?

sorry if its hard to understand what I’m asking! here’s an example:

How would I give proper credit if I use something from a online source such as this (they have sources at the bottom, am I to use those in my paper?):

http://74.125.155.132/search?q=cache:_famzvpvwIYJ:www.improvingoutcomesnetwork.org/downloadDocument.jsp%3Fdocid%3D9+Principles+of+Child+Development+and+Juvenile+Justice+Information+for+Decision-Makers&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a