Mantra Theme Navigation Bar

Hi, I was hoping that somebody may be able to assist me please. I am wanting to build a navigation bar in my new site and I am using the Mantra theme. It automatically defaults to have ‘Home’ and ‘Sample’. I am honestly not quite sure where to start to be able to achieve this and have read various threads but still remain confused. To do this, do I need to use CSS coding? If anybody was able to provide assistance I would be most grateful. Thank you.