<?php
    $firstName = "Martin";
    $age = 21;
    echo $firstName;
    echo "\n";
    // or
    echo "First Name: " . $firstName;
    echo "\n";
    // or
    echo 'First Name: ' . $firstName;
    echo "\n";
    // or
    echo "First Name: {$firstName}";
    echo "\n";
    // or
    echo('Hi All $firstName');
    echo "\n";
    // or
    echo("Hi All $firstName");
    echo "\n";
    // or
    echo $firstName , $age, " years old";
    // no return value
    //$returnVal = echo('hi');
    //echo "\n";
    //echo $returnVal;
?>

Martin
First Name: Martin
First Name: Martin
First Name: Martin
Hi All $firstName
Hi All Martin
Martin21 years old