diffrenet between storing selection into variables

diffrenet between storing selection into variables

hi , i have stored a selection into a variable .take alook at this

      $("#container_show_subject #update");
var $var1 = $("#container_show_subject #update");

i can use attr('id') for the first one and return back the id
but for the second one i can not use an id attr , i dont know why ?
can you give me an example , of how doing it ?