How to call next and previous posts and to assign post name for slug?

In the dashboard, go to “Settings” –> “Permalinks.” Either select Post Name or select custom and type in: /%postname%/

You might also want to strip the category base (url.com/category/postname). To avoid code, use http://wordpress.org/plugins/wp-no-category-base/ or http://wordpress.org/plugins/wordpress-seo/

To display next/previous on the post, you’ll need to modify the php template being used for posts. Check the template hierarchy ( http://codex.wordpress.org/Template_Hierarchy ) to find which template is being used for posts, and read over this as well: http://codex.wordpress.org/Next_and_Previous_Links. This is customization you would definitely want to do in a child theme (http://codex.wordpress.org/Child_Themes). There might be a plugin to handle the later part, but I don’t know that for sure.