It’s a good thing to have a clean, nice and relevant domain-name. Search engines take the name into account when showing search results. If you want visitors to find your site thru the search term “beginner seo” it can be a good idea to register the domain http://www.beginner-seo.com
It’s also important that all pages of your website have a nice URLs. If a page is going to be called “Seo firms” then the url should be: http://beginner-seo.com/seo-firms/. Make sure to use your keywords in the URLs.
As a suggestion the page title can be Seo firms | Beginner-seo.com
<title>Seo firms | Beginner-seo.com</title>
If your building you website in a CMS, like drupal, wordpress, magento, you can usually customize titles and urls so that they are nice and clean.
Do NOT use URLs like: www.beginner-seo.com?s=13245
Make sure your URLs are: www.beginner-seo.com/easy-seo/ (or similar)