First, HCS runs a useful tool called phpMyAdmin at https://www.hcs.harvard.edu/phpmyadmin/. You can view and modify many of your database settings here. You can also access your mySQL database from the command line by typing

mysql -h mysql.hcs.harvard.edu -u group-name_here --password=sql_password_here

at the command prompt.

Some settings you would use in connecting to the database in a php script:
DB = group_name
DBUSER = group_name (same)
DBPASS = your_mysql_password
DBSERVER = mysql.hcs.harvard.edu