This is a pretty simple question (I think), but being brand new to WordPress, I'm still a little stumped...

Is there a way to change the Categories URL from the category number, to the category slug? Like, I choose a certain category in the drop-down box, and it ends on a page that ends in the category number, rather than a more descriptive, prettier category slug.

Basically, I want to change the category pages...

From This: http://myblog.com/?cat=4
To This: http://myblog.com/science-news

This is with Wordpress 3.5.1.