when we use worpress CMS locally do i need to use same database info. (in wp-config.php) as it is on the server, or database info can be different and importing/exporting will not effect?
It can be different. You are only importing and exporting the Wordpress field. The MySQL database settings are outside of that.
The part of the MySQL database that contains all the blog data. You export it as a single file and load it into your local database. Wordpress - Backing Up Your Database