Add & Remove Items from List Using Javascript

Hello,

Over the past week, I have been learning javascript - so if this is a basic question, forgive me. I am trying to create an Add & Remove List. I found some code that will accomplish my objective, and part of that code is displayed below; however, there are a four pieces of the code I do not understand - and one major piece I would like to change. First, what are the $ doing? Second, why is there a colon (:) in front of checked? Third, what is the .is doing? Lastly, why are the + before and after "appID." If you want to see more of the code, you can find it at https://www.pickabundle.com/courses/. For my purposes, I don't need the JQuery or PHP elements - though they are nice touches. I may simply the code a bit by creating "add" and "more info" stationary buttons below my items. The biggest thing I am looking for is the ability to add items from the left to an unordered list on the right that will total up the final cost of the listed items.

<script type="text/javascript"> function bundleRemove(appID) { if($('#check_'+appID+'').is(':checked')) { $('#check_'+appID+'').click(); $('#image_'+appID+'').attr('class', 'icon_normal'); } else { // Do nothing, this app isn't in their bundle. }

Thanks All!