WordPress is a bit different than those two.
It’s an online tool you use to manage your site content as a whole. So really it has two parts, there’s the initial setup where you (or a designer/programmer) sets up how your content will be presented. This would include the look of the site, the navigation you would use to get around, whether you have any static information on the site. Think of it as setting the stage for the content.
The second part is made up of the tools to actually manage your content. Content can be words, pictures, videos, basically whatever you would like. Once your site is initially set up you would just go into the admin panel for WordPress and type your content (or upload your photos, video, etc) and publish it when it’s ready to go. The software would then handle presenting that content to people who visit your site. There’s a lot more to it, like categories you can file content into, tagging, permissions, and content can be generated specifically for all those things.
If you want to change the look of your site at some point in the future, you could do so without losing the content you’ve already put in, although it may be presented differently.
The whole point is to make updating your site as easy as asking a question is here. Then depending on how you set it up, WordPress will handle things like the “Siblings” that are shown next to questions, how many questions to show on a page, the JellyShirt promo, etc. Fluther isn’t run on WordPress, don’t get me wrong, but you could achieve some of the things here fairly easily.
Actually, come to think of it, the Fluther Blog is run on WordPress. And a fine example it is… What you can’t see is the admin section, where andrew and ben could add new articles which would automatically update the sets of links for “Recent”, “Archives”, and “Categories” down the side. Or create new categories, make changes to what shows on each page, etc. The setup part would be what they did initially to tie the design and navigation into the rest of the site.
Good luck with your site.