To make the url text plain and great looking, for example in the beginning a post url will be yoursite.com/?p=20 when changing to post name permalink the url will be yoursite.com/postname.
If you have imported the demo content, you may notice that all the pages are imported but the home page is not still showing as front page. To set the home page as front page, go to Settings > Reading and select the Home as static page.
