mysql databaseand Joomla website localhost linking

[WrinaSellers]

I have a pre existing joomla website.
I downloaded all the files to my hard drive so I could work locally.
I have also downloaded the mysql DB from my hosting account.
I have a plain entry page for the homepage index.php

My joolma site is linked through my homepage(index.php) and nested in a separate file:communitycenter
Example:::localhost/www(mysite.com)/communitycenter (Joomla is nested in the communitycenter folder)

I would like to update and work on the joomla site locally, but I am not able to link the mysql database and the joomla site.
I am able to view the mysql databse for my joomla site, and the initial home page in the root directory, but not able to view the joomla site: communitycenter. (i.e. I do not receive a login screen to access)

The joomla site is in the www directory in the xampp folder. ie: localhost(xampp)/www/communitycenter
My mysql database is localized in the www folder: localhost/www

how do I link the mysql with the php pages/compents/libraries/modules/plugin etc....
so I can work locally????? Help