Internet Advertising comes in many forms.
One such form might include PPC advertising. PPC or (pay per click) advertising are the advertisements you see on popular search engines, and parked pages. PPC ads are generally distinguishable, as near these ads on your browser you may see the words "sponsored by". Pay Per Click ads for the most part, are bid for position advertisements. Advertisers compete against each other for page position for given search phrases or words. Every time you click on of these "ads" it might cost the advertiser, anywhere from five cents, up to forty or fifty dollars per click through. Bid price depends on the competitiveness of the product, service or information that individual advertiser is trying to present to you. Most PPC ads are very light on graphics, and heavy on text.
Another form, and the second most popular by volume of spend are Banner Advertisements. Banner Advertisements can be found on many popular Search Engines, and parked pages. These "ads" would generally be found at the top of your browser, and more frequently as of late are being thwarted by pop-up blockers on different browsers. Depending on your target market these "ads" may or may not be more effective in driving "targeted traffic" to your website. However Banner Advertisements do seem to be a cost effective way to "Brand" your product, service or company. Banner ads use heavy graphics compared to PPC. Banner ads also seem to fall under a different bidding process, most advertisers bid per impression not per click, bids are placed per thousand impressions, upon factors of key words or phrases and demographic that the advertiser is trying to reach.
Classified ads are another very popular form of inter net advertising. Classified Advertising may or may not have cost associated with an ad placed with a popular search engine, or list web site. Classified Advertising can be highly effective and targeted, because an advertisement is shown for one category or sub-category on a given web site or web page, versus PPC or Banner Advertising which may show results under many categories (search terms) and demographics.