Search engine advertising (SEM) involves marketing websites by purchasing paid listings on search engines. Advertisers choose keywords that can trigger their ad and determine where the ad appears based on location, device, etc. Google determines ad rank based on quality factors like click-through rate, keyword relevance, and landing page quality. Advertisers can choose between payment models like cost per click (CPC), cost per acquisition (CPA), or cost per mile (CPM). Organizing accounts into campaigns, ad groups, and keywords helps target the right audiences.