The goal of SEO is to get a web page high search engine ranking. The better a web page's search engine optimization, the higher a ranking it will achieve in search result listings. (Note that SEO is not the only factor that determines search engine page ranks.) This is especially critical because most people who use search engines only look at the first page or two of the search results, so for a page to get high traffic from a search engine, it has to be listed on those first two pages, and the higher the rank, the closer a page is to the number one listing, the better. And whatever your web page's rank is, you want your website to be listed before your competitor's websites if your business is selling products or services over the internet.
Hey Ted, thanks for the great questions! The peak times refer to your particular time zone, if you are targeting an audience that resides in the same zone as you. You can also use tools to find out when most of your audience is online. For example, Facebook has this built into their Page Insights. For Twitter, you can use https://followerwonk.com/. Many social posting tools also offer this functionality.