There are a ton of tutorials online. You may want to search for "writing a php application with mysql" or "php and mysql tutorial"

Essentially you do something like this:

$username="username";
$password="password";
$database="your_database";

mysql_connect(localhost,$username,$password);
@mysql_select_db($database) or die( "Unable to select database");

$query = "SELECT * FROM table;";
mysql_query($query);

mysql_close();