Considering Word Press for your blog or site? Notice there are two different choices, a free blog at wordpress.com or your WP blog on your own host like MediaTemple or GoDaddy, which you download from wordpress.org.
Confused about which one to choose?
In a nutshell, the free version at WordPress.com constrains you to their templates but takes care of hosting and upgrades. The ability to edit the CSS is an add-on for a (minimal) fee. If you are asking “what is CSS” then the free version is enough to do great blogging as long as you can live with a template (the look) that others might be using too.
The version you put on your own host gives you or your designer much more design freedom. It lets you add many more widgets — widgets built by anyone who can figure out how. It also requires you to do the upgrades whenever an improvement or security issue arises. This can be a real hassle if you don’t love spending time hunting down plugin developers and overcoming upgrade incompatibilities that make you site go wonky.
Read a longer list of differences here: