They are different. SEM is search engine marketing, which is the process of improving the visibility and click-through rate of a website in search engine results pages. SEO is search engine optimization, which is the practice of increasing the quantity and quality of traffic to a website from search engines.
Google Ads are a form of advertising that appears as sponsored Links in the sponsored section of Google’s search results page. Google Ads works by targeting users who have previously searched for keywords related to your business or product.