I mean that I have a forum that is also using XenForo,and I want to add a tab to show something,NOT adding tabs at here.
Oh that is a navbar (short for navigation bar), not a sidebar. to do that it's rather simple. because of my lack of knowing your ability and the fact you had to ask, I don't really feel like explaining it in more detail so I am going to suggest an addon for you. here it is. http://xenforo.com/community/threads/product-xenfans-com-extra-tabs.19606/