To recap, your "Structure" defines which "Web Containers" go where.
"The Look and Feel" defines the Colour and size of your websites component parts.
Your "Homepage" defines which "Functionality" you want in each container.
It will save you time if you familiarise yourself with the range of functionality available to you, because once you have chosen what to put where, this, including any copy, will be copied to subsequent pages. It can of course be changed, but changes are time consuming.
Adding new pages is exactly that, you should remember that whilst your chosen structure (Containers) is fixed for your site, the functionality or Widgets that you choose to put in each container is not.
Adding a page will however copy the widgets and any copy or pictures from the homepage.
Pages are main menu items, Subpages are menu dropdown items.
Subpages have the same characteristics as Pages. (See Add a New Page)