There are several methods of connecting to a database, here’s one example:

// Set the database access information as constraints
DEFINE ('DB_USER', 'userName);
DEFINE ('DB_PASSWORD', 'passWord');
DEFINE ('DB_HOST', 'localhost');    
DEFINE ('DB_NAME', 'databaseName');   

Use DEFINE to set your login details, then:

// Make the connection
$dbc = @mysql_connect (DB_HOST, DB_USER, DB_PASSWORD) OR die ('Error: Check UN, PW, and host ' . mysql_error());

Connect using mysql_connect, then:

// Select the database
@mysql_select_db (DB_NAME) OR die ('Could not connect to database: ' . mysql_error() );

Select the batabase to use…

Once that’s done, you can write SQL queries like:

$query = "SELECT * FROM tablename WHERE conditions";
$result = mysql_query($query);

if(mysql_num_rows($result) != 0) { // if results are found
    while($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
        $var1  = $row['col1'];
        $var2  = $row['col2'];
        $var3  = $row['col3'];
        // etc...
    } // end while
} // end if