how to get dynamic value into the database

I'm a beginner in PHP, this is my code

<h3 class="green">Generate Report</h3>
    <p>Please select the date range of the report you wish to print.</p>
    <form id="generate-pdf" action="print.php" method="post">
<table class="activate-res">

    <tr>
        <td><p class="form-type-left">Course Activity:</p>
            <select id="" name="courseActivity"   class="dropdown" >
                <option value="">--Unspecified--</option>
                <option value="all">All time</option>
                <option value="7">Last 7 days</option>
                <option value="30">Last 30 days</option>
            </select>
       </td>
    </tr>

</table>



<?php if (isset($_SESSION["site_admin"]) && (int) $_SESSION["site_admin"]) { ?>

        <h3 class="green">Select site(s)</h3>
        <p>Please select which sites to include in the report.</p>

<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
$('#select-all').on('change', function() {
  $('.listSite input[type="checkbox"]').prop('checked', this.checked);
});
$('.listSite input[type="checkbox"]').on('change', function () {
  var allChecked = $('.listSite input:checked').length === $('.listSite input').length;
  $('#select-all').prop('checked', allChecked);
});
});//]]> 

</script>

<table class="err_highlight activate-res" style="border:1px solid #fff">
    <tr>
        <td><input  type="checkbox" value="All Sites"  id="select-all"  name="selectSite"></td> 
        <td>All Sites</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Chilterns"></td>  
        <td>Chilterns</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Fakenham"></td>   
        <td>Fakenham</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Grimsby"></td>    
        <td>Grimsby</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Head Office"></td>    
        <td>Head Office</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Headcorn"></td>   
         <td>Headcorn</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Histon"></td> 
        <td>Histon</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Killingbeck"></td>    
        <td>Killingbeck</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Luton"></td>  
        <td>Luton</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Waterside Park"></td> 
        <td>Waterside Park</td>
    </tr>
    <tr>
        <td  class="listSite"><input name="selectSite" type="checkbox" value="Westwood"></td>   
        <td>Westwood</td>
    </tr>
</table>

<?php } ?>

<!--   onClick="document.location.href='template.php'"  -->
<table class="activate-res">
<tr>
    <td><input name="submit" type="submit" value="Generate Report"  class="log-button"  /></td> 
      <td><input name="cancel" type="button" value="Cancel"  class="log-button" onClick="document.location.href='admin-serials.php'" /></td>
</tr>
</table>
</form>

</div><!-- content -->
</div><!-- wrapper -->

<?php include('footer.php') ?>

This is my data generate code but this static i want to dynamic output how can b possible to change? if i select all then they get and display all site data from to database or if i select 7 or 30 day then they get and display to 7 or 30 days data, and the following 10 site show in static but they also change in dynamic if i check the checkbox all or i choose selected then click to generate data. It means i m select Westwood then they get data only westwood or i m select all then they get all data display.