To set up and customize menus, 

• Go to Admin Dashboard > Appearance > Editor
• Now, click on the ‘Template Parts’.
• You will see a menu option in the tab where you can edit it from. 

To set up navigation,

• Log in to the WordPress admin Panel.
• Go to Appearance > Editor
• Click on the blue ‘+’ symbol on the top left.
• Now, search for ‘navigation’.
• Add or remove the navigation you prefer and you are good to go.