I've got a website with about 170 pages and I want to create an effective Sitemap for it as it is long due. The website is internally linked very well but I still want to take advantage of creating a sitemap to allow SE's to crawl my site easier and to hopefully increase my websites PR. Though I am slightly confused to what I must do: Is it necessary to create a .xml sitemap AND a HTML Sitemap (both)? ... Because I've never worked with .xml ... where do I put this file once it's created? In the Root folder? So I assume that this sitemap.xml is ONLY to be read by spiders and NOT by website visitors. IE: No visitor on my website is going to visit the page sitemap.xml, am I correct? ... Hence why I should also create an HTML sitemap (sitemap.htm)?
Normally no user will see your sitemap.xml, it's there for the robots and spiders, you're right. You put it on the root directory of the site.
In theory, a sitemap.xml should be enough, no need of a sitemap.html... but sitemap.html are useful for SEO, and some users like to use them to navigate the site. If you do a sitemap.xml, the .html can be automatically generated from the xml, you don't need to pass a lot of time to generate it, so IMHO you should still do both of them.