Please open the fiddle and read the comments to understand the concept or just copy paste it and use it. As simple as that

How to use jQuery with JavaScript
https://fiddle.jshell.net/5rq261hp/

jQuery On-Click function make alert
http://jsfiddle.net/X4WtG/170/

jQuery On-Click opens a div
https://fiddle.jshell.net/4w2swgvL/

JavaScript replace the text using document.getElementById
https://fiddle.jshell.net/8upuaofg/2/

How to declare variable in JavaScript
https://fiddle.jshell.net/L5ahawt4/1/

How to get output in jQuery using dropdown and onchange function
https://fiddle.jshell.net/ex6m6a6f/1/