The importance of being visible on the Internet is a high priority, while a web or store without SEO or SEM would be the same as a local business which customers do not come.
SEO: Technical and series of steps that help improve the visibility of your website in search results of search engines organically. A medium-term process, but effective and durable.
SEM: Paid advertising provided by the same search engines, increase your web traffic immediately. The SEM unlike SEO when the contracted service once decreases the traffic ends.