Here a js part:
function getinfo() {
var aList = document.getElementById("select");
var val = aList.options[aList.selectedIndex].value;
// document.write("<p>Here what you select: "+val+"</p>");
// here you can send `val` to the server using... are you using any js library?
}
And you need to change your select declaration:
<select name="select" id="select" style="width:50px;" onchange="getinfo()">
--------------------
</select>
OK, how to send val to the server is another question... If you are using jQuery - you can use jQuery.ajax(...) or any helper like jQuery.get(...). If you are vanilla-js user you can use XMLHttpRequest way and if you use any other lib - just check this lib's documentation to get helped about sending data to the server.
changehandler.