Simply put yes you should have a site map for your website, in fact you should have two Apart from a general HTML site map you should also have a XML site map, the latter is for Google and other search engines and spiders. An XML site map gives a short cut as it were to allow search bots & spiders to better index your site.
A XML site map should be place in the root of your site directory, once set up, you can go to Google web master central and add the site map to your website.
If you have not set up your site in Google web master central you should also do this, it provides useful statistics and tools designed to better rank and gain better targeted traffic to your website. It also can inform you on problems your site may suffer from. These problems could be, parts of your site that are unable to be indexed, duplicate content issues, not found errors and more.
Check out Google web master central today and better understand your site.