html - not receiving emails from php mail() function

I have recently been learning HTML, js, CSS, and PHP
through creating web pages and posting them on my apache2 server hosted on my raspberry
pi with a no-ip.com address. My first real project for learning PHP has been creating a
simple form to then send an email to me, but I keep running into the issue of the mail()
function executing without any errors, but not actually sending
emails.

Here is the
form:

            action="/FormTesting/sendMail.php" method="post">
 Name:            />
 Email:            />
 Message:            />            required>
 Subject:
             name="subject" value="Hello!">Hello!
             value="Whats up">Whats Up!

             name="submit"
            value="Submit">

Here
is the PHP file reference in the form's 'action'
attribute:

if($_SERVER["REQUEST_METHOD"]
            == "POST") {
 $to = "myExampleEmail@gmail.com";
 $name =
            $_POST["name"];

 $email = $_POST["email"];
 $message =
            $_POST["message"];
 $subject = $_POST["subject"];

 echo
            $name;
 echo $email;
 echo $message;
 echo
            $subject;

 $headers = array("From: " .
            $email,

"Reply-To: " . $to,
"X-Mailer: PHP/" .
            PHP_VERSION);

 mail($to, $subject, $message,
            $header);

} else {
 echo
            $_SERVER["REQUEST_METHOD"];
}
?>

I
understand that this question has been asked before, and I have tried most of the
methods set out by other answers, but I still can't seem to get the PHP mail() function
to work. The best information I have is that I have to do some kind of install or
formatting on the server itself to allow for emails to be sent, but I have yet to find
it well documented and/or explained. (i.e phpMailer? - but still...
how?)

EDIT:

I
checked the return value of the mail function . . .

            if(mail("myExampleEmail@gmail.com", "subject", "message", $headers)) {
 echo
            "TRUE";
 }else {

 echo "FALSE";
 }
            

. . . and it turns
out to be returning false. I assume that means it is an error in my code,
then?

EDIT:

Apparently
I wasn't clear when I said I did research before posting this question. I tried
everything that was given as an answer to the question that mine was a closed as a
"duplicate" of, hence me asking, the question anyway.