This one can be frustrating - you're working hard on your Joomla site and suddenly your front page content doesn't show!  First, check and make sure you've got a link to the Frontpage component in the Main Menu - and be certain it is published. 

If you decide you want a "top" menu rather than a left or right column menu, simply use the "main menu' as the source for your chosen menu (yes, you have a 'top menu' but Joomla likes the main menu to be the "main" menu)

Now, you may still have issues getting your homepage content to show - check and make sure the 'Home' link is at the top of your list - if another link comes before it, then you won't be able to see your content.  It isn't enough (unfortunately) to just create a link to "/" or 'http://www.mywebsite.com' - you have to create a component link and select the Front Page component.

I know it's confusing, but give it time and you'll start to understand how the menus work.