SEO and SEM are often confused
Search Engine Marketing: SEM is buying AdWords (or other paid internet promotion advertising such as banner ad campaigns). Search engine advertising is extremely manageable. You choose what you wish to invest, which keywords or keyword phrases you wish to buy, and exactly which webpage you would like link your ad to.
In the image below you can see the paid SEM results highlighted in RED
Search Engine Optimization: This is where San Francisco SEO specialize. SEO is the assessment of an internet site in order to uncover any kind of technical limitations that could be preventing search engines from being able to access a web-site’s information, then identifying the best related site content and enhancing essential features in order to assist the internet search engine to index your content most appropriately.
In the image below you can see the ‘natural’ or ‘organic’ SEO results highlighted in BLUE