Search Engine Optimization is like an Pine tree. The time and money invested in optimizing your website will continue to bring you results for as long as you have the site.
Today, a good SEO strategy is incomplete without a social component, and a good social media strategy contributes to your SEO initiative. Each network has a niche that it's best suited for and some media types work better than others for different markets.
Paid search allows you to pay a fee to have your website displayed on SERP when someone types in specific keywords or phrases to the search engine.