I need to open my database through PHP but I need to know my username and the name of my localhost, and i don't know them.
When i used mysql and did my database it just asked me directly for a password.
The default username is root. You can reset the root password if you do not know it: http://dev.mysql.com/doc/refman/5.0/en/resetting-permissions.html. You should not, however, use the root account from PHP, set up a limited permission user to do that: http://dev.mysql.com/doc/refman/5.1/en/adding-users.html
If MySql is running on the same computer as your webserver, you can just use "localhost" as the host
type this command