DreamHost does not have a "sitebuilder" tool, but all the capabilities you need to build a website are available to you.
There are a couple of ways you could approach this:
1) You can build your website in html, and/or php, and upload it to your webspace on DreamHost. A good introduction to this process in the DreamHost wiki article on Building A Website and in many tutorials you can find referenced in that article and other places on the internet (you can find them via a Google search.)
2) As the article mentioned above states, you can also use the DreamHost "one-click" installer to "automagically" create a website using your choice of several web applications. WordPress, while originally and primarily a "blogging" tool, has the ability to make "pages" also and, as such, is a very serviceable "website builder" as well (it also comes with a very large selection of designs (templates), and there are thousands more freely available on the web.
There is also the Joomla! CMS system, which is a little more difficult to learn, but is also more powerful. While it does not come "out of the box" with as many different designs available at install time, there are also thousands of "designs" freely available for it.