How Indexes Work

How does the stock market and how to trade / invest in it?
I want to start trading or investing in the stock market, but really not understand the terms, such as indexes, averages, etc. I do not know how the whole stock market. Someone I can summarize or provide a Web site listed? Thank you.
www.betterinvesting.org
Excel Magic Trick #27: VLOOKUP won’t work: use INDEX & MATCH