Imma got lazy when I had to type the <div class="mw-collapsible mw-collapsed"> stuff, so I went ahead and make a template for it.
Since I am newb, I haven't really included how to use this template or what it is used for, here it is.
| header= (header name)
| content= (content infromation)
That should work when it comes to that. So then you should get the finished product of a collapsible header. (That's what Imma call it so, heck...)