Adwords is the premier advertising product of Google which is responsible for most of their revenue – In 2010 alone, revenues were $28 Billion :0
Google Adwords is a PPC (pay-per-click) engine meaning you only pay when someone actually clicks your ad. The opposite (and more traditional) of this is CPM advertising, where you pay a certain rate regardless of how many clicks you get.
There are TWO sides to Google Adwords – The Search Network and The Content Network.
Google Search Network
The Google Search Network is composed of the familiar Google SERP page we are all familiar with. The idea is that advertisers can bid on keywords that trigger their ads when a user performs a search. If you sell perfume online, then some likely keywords you would include in your keyword list is “perfume” and “cologne”.
Google Content Network
The Google Content network is the sum total of all the webpages on the internet that have Google Adsense installed on them. It is the biggest advertising network on the planet at the time of this writing. By allowing webmasters to place Adsense code on their websites, the amount if traffic available increased ten-fold.
There are 2 types of ads you can run on the Google Content Network – text ads and image ads (ie banners). Text ads are the same format as Google Search ads, and Image Ads are available in all the standard IAB sizes.
Sign Up Page: http://adwords.google.com