Can you describe the purpose of people I see on NYSE trading floor on
TV in details? A comprehensive one please, with picture would be
great!

Does it matter whether I invest stock in NYSE or NASDAQ? What are the
difference betwene the two?

Different stocks are listed on either of the exchanges. 

Depending on which stock you invest in, you will be investing on a
NASDAQ traded stock, or a NYSE traded stock.

People running around the floor can be doing a number of jobs.  Go to
the various exchange websites and look up careers on Wall Street.  It
is a very complex process.

http://invest-faq.com/cbc/exch-nyse.html
http://invest-faq.com/articles/exch-nyse.html

Many people are the floor are "floor brokers."  They might be running
around because they have a large institutional order to fill.  Your
nyse order will likely be routed through the computer network.  The
specialist is still in control of the fills, but the computer does
much of the buy/sell matching.  The naz is one giant computer network.
 It does not have anyone running around anywhere.

And there are many, many more aspects more important than whether a
stock that you buy is nyse vs nasdaq, such as your overall investment
goals, diversification, and risk tolerance.  In general, the naz tends
to be newer companies and tends to be more tech-oriented.  The listing
requirements for the nyse are more stringent, so those companies tend
to be bigger and older.  But *do not* read this to mean that the nyse
stock is safer than the nasdaq stock.  It is just as easy to lose
money in either market.