Search engine advertising (SEA) is a type of online advertising that involves placing ads on search engine result pages (SERPs), such as Google or Bing, when someone searches for a specific keyword related to the product or service being offered.

Here’s how it works:

1. Advertisers create ad campaigns and choose keywords they want their ads to appear for on the search engine.
2. The search engine then uses an auction-based system to determine which ads to display and in what order, based on factors such as the advertiser’s bid, the relevance and quality of the ad, and the user’s search query.
3. When a user searches for one of the keywords the advertiser is targeting, the advertiser’s ad may appear at the top or bottom of the SERP, or as a sponsored listing on the side of the page.
4. If the user clicks on the ad, they are taken to the advertiser’s website, and the advertiser is charged for the click.

Pros of search engine advertising include:

1. Targeted reach: Ads can be targeted to specific keywords, demographics, locations, and other user behavior, allowing advertisers to reach a highly-qualified audience.
2. Measurable results: Advertisers can track the performance of their ads and make data-driven decisions about their campaigns.
3. Flexibility: Advertisers can set budgets, adjust bids, and target specific keywords, allowing for complete control over the advertising campaign.
4. Quick results: Unlike other types of advertising, results from search engine advertising can be seen quickly, making it a good option for businesses looking for fast results.

Cons of search engine advertising include:

1. Competition: The competition for top positions on the SERP can be fierce, and getting a high ranking can be difficult and expensive.
2. Cost: The cost per click (CPC) for search engine advertising can be high, especially for popular and competitive keywords.
3. Complexity: Running successful search engine advertising campaigns requires a good understanding of search engine algorithms, keyword research, and ad optimization.
4. Lack of brand awareness: Search engine advertising is focused on driving targeted traffic to a website, but it may not be as effective in building brand awareness compared to other types of advertising.
   

Here are some of the main search engine advertising platforms:

1. Google Ads: Google Ads is the most widely used search engine advertising platform. Brands can create text, display, and shopping ads that appear on Google search results pages, as well as on Google’s network of partner websites.
2. Bing Ads: Bing Ads is the search engine advertising platform for Bing, Microsoft’s search engine. Brands can create text, display, and shopping ads that appear on Bing search results pages, as well as on Bing’s network of partner websites.
3. Baidu Ads: Baidu Ads is the search engine advertising platform for Baidu, China’s leading search engine. Brands can create text, display, and shopping ads that appear on Baidu search results pages, as well as on Baidu’s network of partner websites.
4. Yahoo Gemini: Yahoo Gemini is a platform that allows brands to place ads on both Yahoo and AOL search results pages. Brands can create text, display, and shopping ads that appear on both Yahoo and AOL search results pages.

These platforms use a pay-per-click (PPC) pricing model, where brands pay each time a user clicks on one of their ads. This allows brands to control their advertising costs and only pay for the traffic they receive.