Permalink is the url form which people see on the address bar when they have clicked on the links pointing to your website. Its better if you follow the proper kind of permalink structure from the beginning itself and in that way you need not change the url structure for more Search friendly url structure in favour of Google Panda and Penguin algorithm updates. By default the permalink structure of WordPress blogs is
which is not at all good as per Google’s updates and not even visually appealing.
Experts prefer two kinds of permalink structure one is using the custom structure and keeping the url as category/post name and the second one is the post name which I have used for seekdefo also
In addition to using this kind of permalinks use hyphen(-) instead of underscore( _). They are the standard and search engine friendly too.
To change the settings just go to the permalink settings option of your dashboard.