They are normally called friendly/clean/custom url’s. In Settings -> Permalink Settings WordPress states,
By default WordPress uses web URLs which have question marks and lots of numbers in them, however WordPress offers you the ability to create a custom URL structure for your permalinks and archives. This can improve the aesthetics, usability, and forward-compatibility of your links. A number of tags are available, and here are some examples to get you started.
You will need to turn these on for the plugin to work. I would also note that the plugin is rather advanced and will require a thought out workflow when using on your website.