Most website visitors browse a website's homepage quickly. They are interested to see if there is any reason for them to go deeper into the website. They generally want to find information quickly and clearly without being confused by irrelevant distractions.
When a website visitor has progressed from the homepage they need to be led to the next page that will interest them or towards a point of action. If there is no such structure or focus on usability the chances are, the visitor will leave the website without benefit to themselves or the website owner.
Website Navigation & Structure points to consider:
The depth of the website / number tiers of links
How the website is subdivided into groups and pages
The ability to navigate to any other page on every page
The style of navigation; Embedded Links, Navigation Bar or Breadcrumbs
A structure that is friendly to search engine indexing
Consideration of leading to a call to action EG, Call Us, Sign Up, Email Us etc.