Go to Dashboard => Appearance => Menus:
Now click the create a new menu link:
Next, name your menu (you can choose anything you want to remember it with). Then click Create Menu button:
From the left side you’ll have your pages/posts to choose from, if you want to add a page, open the pages panel and select the page you want to add to the menu, then click Add To Menu. You can do the same with posts, projects and categories or even add your custom links. When you finish adding your links, make sure you check the Secondary Menu box in the Menu Settings section. Now click Save Menu button:
And you’re done! Check the front page of your site.
Please check also: How to Add Navigation Menu in WordPress (Beginner’s Guide)