The hostname to connect to is "localhost" if connecting from a script on the server, or your domain name for connecting remotely. The database name and username need to be entered exactly as they appear in the MySQL manager in your control panel (CPanel) ie cpanelusername_dbname, etc. The password is the one you specified when creating the username.
When you create a username in cpanel, please be aware that there is an 8 character limit. Extra characters will be dropped.
Also, you can have more than one username for a database. If you forget your user password, you may either find it in the script's config file or add a new user to the database and edit the script's config file.
Please make sure you have added the database user to the database. You must select the user and the database from the drop-down lists and then click on the "Add User to DB" button. You should see connection code provided if you have done this.
For best results if connecting remotely and if you do not have a static ip address, you need to add a single % sign to the access host list in the MySQL manager of your cpanel.
The port is 3306.