A great way to see exactly how existing websites function and operate is by checking out various services online in which websites are being sold.  When a website owner wants to sell their website, the only way they can sell it is by providing essential details about how much money the website makes (gross and net), how much traffic it receives and from where, and how exactly the website makes its money.

    A popular website which facilitates the buying and selling of websites is Flippa.com.  There's a "Just Sold" tab on the home page where you can check out websites that were recently just sold, and consequently view all of the details about each sale.  Here's an some examples from this list.

• BestPhotoshopTutorials.net
  
  Sold for: $2,800
  Earns: $415 per Month
  80,000 Unique Visitors per Month, 250,000 Page Views per Month
  47,936 Alexa Ranking
  
  This is a website that offers free photoshop tutorials and photoshop brushes.  Photoshop is popular design software from Adobe.  This website earns its money as a publisher.  It provides free content to visitors, and advertisers can purchase banner spots through BuySellAds, and Text-Link-Ads.  He also uses Google Adsense to place banners throughout the site.
  

    Because Flippa only lists a limited number of "Just Sold" sites, you can browse the much larger currently in-progress auctions and view details of websites that way.  You can visit this link to view websites that are in auctions that end very soon.  Here are examples from this list:

• Learning-Styles-Online.com
  
  Current Bid: $16,700
  Earns: $600 per Month
  62,800 Unique Visitors per Month, 408,700 Page Views per Month
  370,580 Alexa Ranking
  
  This is a unique website which helps instructors / teachers understand and analyze different learning styles.  This site makes its money as a publisher through Google Adsense.  It receives traffic through search engines by SEO.
  
  
• CompletePersonalDevelopment.com
  
  Current Bid: $2,200
  Earns: $400 per Month
  4,500 Unique Visitors per Month, 60,000 Page Views per Month
  484,015 Alexa Ranking
  
  This is a self help / education website that earns money as a publisher, primarily through Google Adsense.  It also makes money through affiliate marketing with Clickbank.
  
  
• Twitart.com
  
  Current Bid: $1,800
  Earns: $1,700 per Month
  1,000 Unique Visitors per Month, 1,200 Page Views per Month
  536,882 Alexa Ranking
  
  This is a custom design service specifically for creating twitter backgrounds.  It earns its money as a service based website.
  

    Feel free to browse around more on Flippa to see exactly how websites are making money.