Adding new pages to Menu

Go into the dashboard and then to the pages menu. Add a page, give it a title of About Us. Do this for as many pages as you need.

Then go to Appearance > Menus

On the right fill in the Menu Name, you can name it anything (i.e. Main Menu, Primary)
Over to the left you should see a box that says Theme location, depending on the theme there may be several drop downs. Pick the first one and select the name you just created on the left. Next scroll down a bit on the left you should see Pages with a list of the pages you created. Click and check the boxes of the ones you want in your menu. They will appear in the right. You can drag and drop these in the order you like. Be sure to save.