What is SEM? How to do it efffectively?

SEM is a type of Internet marketing associated with the researching, submitting and positioning of a website within search engines to achieve maximum visibility and increase your share of paid and/or organic traffic referrals from search engines.

SEM involves things such as search engine optimization (SEO), keyword research, competitive analysis, paid listings and other search engine services that will increase search traffic to your site.
Search Engine Marketing (SEM) is a type of marketing which is based on the promotion of the website by enhancing its visibility in search engine search pages. It is a paid technique of the marketing where you need to invest some amount for posting ads of your website.
All the marketing tools related to the online marketing are included in SEM (Search Engine Marketing). SEO optimization, link building, and other tools come in this field. Huge organizations have a team who deals with the SEM purposes of the website. Am I right?