Login to your dashboard and then go to:
Appearance >. Menus
Now do the following:
1) Give a name to your Menu - Standard
2) Select the primary Menu - the one you just created
3) Under pages Click select All
4) Click on "Add to Menu"
5) Now drag and drop the menu on the right hand side to place them in some form of order. See this picture:
the sub-Menus are slightly indented as you can see in the picture.
6) Make sure you keep clicking on Save or Save Menu buttons at each stage.
Hope this gives you an idea but always post back to get further help or to learn about official documentation.