Before you add menu or navigation to your blog, make sure you have created the Pages you needed (click here if you need tutorial to create a page).
If you want to have categories page in your menu, make sure you already created the categories too (click here for tutorial creating new category).
- Go to Appearance – Menus
- Give a name for your menu (example : Top Menu)
- Select the pages / posts / categories from the left panel and drag it to the right panel to create the menu structure.
- You can also place custom link to the menu.
- Select the display location for the menu (Usually Primary Navigation)
- To create a drop down menu, just drag the items under the parent menu. See animation bellow :