Everything under the header disappeared

First off, I’m an idiot. This is my first experience with WordPress and I clearly don’t know what I’m doing…So I spent hours making a homepage using the SmallBiz template and was very happy. Then I decided to change the menu names and did something wrong. For a while the page would show up as I wanted when I was logged in, but once I logged out and checked online it would say “Page Not Found” (it had been showing previously). I have now spent so much time trying to correct what I did wrong, I fear I’ve made it all worse. I have no idea what the original settings were under Pages and Menus and don’t know what to do. Help!