Jquery: Append div only once 'on click'

Use a conditional to determine if it's there.

$("#nextractorapply").click(function () {
    if($('#nextractor').length < 0){
        $("#main").append('<section id="nextractor" class="five"> </section>');
    }  
});

You can use some kind of a condition that prevents its appending multiple times.

var counter=0;
$("#nextractorapply").click(function () {
    if(counter<=0){
        $("#main").append('<section id="nextractor" class="five"> </section>');  
        counter++;
    }

    //YOUR OTHER STUFF THAT YOU NEED TO EXECUTE ON EVERY CLICK
});

You could use one(), which fires only once

$("#nextractorapply").one('click', function () { 
    // executes only once

     $("#main").append('<section id="nextractor" class="five"> </section>');  
});

$("#nextractorapply").on('click', function () { 
    // executes every time

    // do other stuff
});