I need to enable form (it is disabled on page load) after checkbox checked

I need your help here cause I am not aware of javascript or jquery library and i think i definitely have to use them in my project.I have a disabled form when the page loads and I want to enable when I checked on the check box.I tried a lot but I didn't find any solutions..

Here is the 'disable' code when the page loads:

$(document).ready(function (e) {
  $("#form1 *").prop("disabled", "disabled");
});

The checkbox is :

<input type="checkbox" id="checkbox" name="opt[]" value="'.$points.'">

If you have any ideas please inform me!

One shot but ..no result was:

document.getElementById('checkbox').onchange = function() {
  document.getElementById('eksargirwsh').disabled = this.checked;
};

form code:

 <form method="post" id="eksargirwsh" action="update_points_test2.php">

           <div class="col-lg-4">
               <div class="ibox float-e-margins">
                    <div class="ibox-title">
                                    <h5>Form1</h5>

                                </div>
                                <div class="ibox-content">

echo '

                                    <div>
                                        <div class="feed-activity-list"><div style="border: 0.5px solid green; border-right-style:none;" class="input-group m-b"><span class="input-group-addon"> 
                                                <input type="checkbox" id="checkbox" name="opt[]" value="'.$points.'"></span>
                                                <input type="hidden" name="opt2[]" value="'.$row_select4['id'].'">


                                          <div class="feed-element">
                                                <a href="profile.html" class="pull-left">
                                            <img alt="image" class="img-circle" src="'. $row_select4['image_url']. '">
                                                </a>
                                          <div class="media-body ">
                                         <div class="ibox-tools">
                                                        <span class="label label-primary">ΔΙΑΘΕΣΙΜΟ</span><br><br>
                                                        <span class="label label-warning-light pull-right"><strong>'  .$row_select4['points'].  '</strong> Πόντοι</span>
                                                    </div>
                                                    <strong>'  .$row_select4['title'].  ' </strong> '   .$row_select4['description'].  ' <br>
                                                    <small class="text-muted">Διάρκεια: <strong>'  .$row_select4['start_date'].  ' - '   .$row_select4['end_date'].  ' </strong></small>
                                                    <div class="well">
                                                        '  .$row_select4['description'].  '
                                                    </div>
                                                  </div>
                                                </div>
                                            </div>

                                       </div>'  ;

 <button type="submit" id="submit" class="btn btn-w-m btn-primary">SUBMIT</button> 
                          </form>