header template of the theme consists of code like below
<li><a href="{$mybb->settings['bburl']}/misc.php?action=help" class="help">{$lang->toplinks_help}</a></li>
required new link code can be added after above code in a similar method
<li><a href="url of the required link" class="something">link_name</a></li>
Yes I suppose, this is what I used for my theme, not sure if it does for yours.
<li><a href="{$mybb->settings['bburl']}/index.php"><i class="icon-white icon-home" style="font-size: 15px;margin-right:2px;"></i> Home</a></li>
Feel free to edit it to your liking.
How to change the icon from the code provoded by you?
Do: icon-example
What kind of icon do you want it changed to? Not sure if you will need my theme lol
Can you give me link of your website let me take a look
This is an easy way to add an image into a custom link in your menu:
<li><a href="linkurl"><img src="imageurl">Link Name</a></li>
You can also change the size of the image by doing this:
<li><a href="linkurl"><img src="imageurl" width="20" height="20">Link Name</a></li>