Simply ut allows users to creat a thread in their desired foeum with desired prefix. 

How to use :- 

1). creat a clickable button on the index page or in the header page under navigation , link should be :- www.website.com/new.php     or       {$mybb->settings['bburl']}/new.php 

2). if you want to have a button under the navigation then here is ths tips.

After install add this css to your theme in global.css or creat a new css named newthread.css and add this .

.newt {
padding: 8px 18px;
border: 1px solid #000;
	box-shadow: rgba(0, 0, 0, 0.16) 0px 3px 6px, rgba(255, 255, 255, 0.23) 0px 3px 6px;
border-radius: 4px;
background: #fff;
color: #fff;
font-size: 16px;
font-weight: bold;
text-align: center;
text-transform: uppercase;
margin-right: 5px;
letter-spacing: 1px;
text-decoration: none;
margin-bottom: 10px;
}

.newt:hover{
background: #0485db;
color: white;
text-decoration: none;
}

a .newt {
text-decoration: none;
}

and then open your header template and in the end add this code

<div><a style="float: right;" class="newt" href="new.php"> New thread </a></div>

Note:- The plugin author is  Edson Ordaz with the original mybb 1.6 plugin submission https://mods.mybb.com/view/new-thread . The only change I have done is bringing the plugin up-to-date for MyBB 1.8 and add some extra features with fuxed some bugs.