Vitamin is about SEO, speed and security. It includes sitemaps for SEO, cache for speed, antispam and hacker blocks for security.
Vitamin helps Google and other search engines to find all of your pages by robots.txt and sitemap files. It saves all information about images, styles or any other files, that was not found. If you enable fast 404 mode, you may speed up your site even if you have some problems on it.
Server cache is a mechanism for the temporary storage (caching) of HTML pages, to reduce server load and reduce loading lag. When somebody open your page, this page is sended to him. But there is also created a copy of it. When second visitor open same page, saved copy is send without slow rebuilding.
Browser cache is mechanism for the caching files like images in browser. If someone visit site, all images in design are saved into browser cache. Second visited page is loaded faster, because browser does not ask for images, that was loaded before. But it works only on better server or with Vitamin.
There are a few default rules or you may add new to block all bad guys, which want to hack your site.
Inappropriate words, comments where are 1000 letters in one word and other trolls comments are blocked.
Please, see Vitamin manual section to set everything right.