SEM ads that appear in Google, Bing and other search engines are text ads

They’re listed at the top or sides of the *SERP.

Paid ads can either be Pay Per Click (PPC) or Cost Per Thousand (CPM).

Unpaid form by optimizing your website for keywords (also known as SEO). Search engines list the unpaid results based on relevance so improving the SEO of your site means you’ll be able to get more hits for free if you improve your site’s SEO.