By default, sites are set up to automatically add any new top-level pages to the main menu. In most cases, this will be sufficient, but if you want more control you can find menu options in your dashboard, under Appearance > Menus.
Your site has two menus. The main menu is where you set up the navigation of your site, so select it to begin editing your menu.
On the left, you can select the items you want to Add to Menu, and as you do, they’ll automatically appear in the Menu Structure on the right side.
Once items are in the Menu Structure, you can drag them around, create a hierarchy by nesting them inside each other, it’s mostly up to you. Just bear in mind, simplicity is always best!
The other menu
The Meta menu is the smaller menu which appears under the main menu. It contains a few things by default, but any items you add will appear before the default items.
Don’t use this menu for navigation. Definitely don’t create a hierarchy of items in this menu.
Use it for links to resources that a visitor might reasonably want quick access to when they’re viewing your site, but don’t overuse it. A good example might be a closely related research site.