$header ="From : $_POST['imie'] < $_POST['email_nadawcy'] > ";
            
            $to ='twojmail@mail.com';
            $subject ="Temat : $_POST['temat']";
            $wiadomosc ="Treść Wiadomości : $_POST['tresc']";
            
            mail($to, $header, $subject, $wiadomosc );

<?php
$form="<table>
      <form method=\"post\" action=\"index.php\">
      <tr>
      <td>Imię i Nazwisko</td><td><input type=\"text\" name\"imie\" size=\"60\" /></td>
      </tr>
      <tr>
      <td>E-Mail :</td><td> <input type=\"text\" name=\"email_nadawcy\" size=\"60\"/></td>
      </tr>
      <tr>
      <td>Temat :</td><td> <input type=\"text\" name=\"temat\" size=\"60\" /></td>
      </tr>
      <tr>
      <td>Tresc :</td><td> <textarea name=\"tresc\" rows=\"10\" cols=\"57\"></textarea></td>
      </tr>
      <tr>
      <td>Anty Spam:</td><td>(token)</td>
      </tr>

      <tr>

      <td>Wybierz: </td><td><input type=\"submit\" name=\"wyslij\" value=\"wyslij\" /></td>

      </tr>

      </form>

      </table>";

    if($_POST['wyslij'])
    {
        if(!$_POST['imie'] && !$_POST['email_nadawcy'] && !$_POST['temat'] && !$_POST['tresc'])
        {
            echo "<span style=\"color: #FF0000; text-align: center;\">Wypełnij wszystkie pola formularza!</span>";
        }else{    
            
            $header ="From : $_POST['imie'] < $_POST['email_nadawcy'] > ";
            
            $to ='twojmail@mail.pl';
            $subject ="Temat : $_POST['temat']";
            $wiadomosc ="Treść Wiadomości : $_POST['tresc']";
            
            mail($to, $header, $subject, $wiadomosc );
        }
    }else{
        echo $form;
    }

?>