There are lots of factors which influence the usability of your product. So, which components have an influence? First of all, the product itself – how can you interact with the system, how does it feel, what does the system give you back? What comes with the product – e.g. manual, accessories, packaging? All this and many more topics are addressed in this article http://www.uselog.com/2010/05/1-usability-101-understand-what.html