Inside the WordPress dashboard navigate to Appearance – Menus. Type the name of your menu and click on “Create menu”. For the main menu, make sure that the Primary Navigation under Display location is checked.
From the left side you can add links to Pages, Posts, Categories or create custom links.
If you want to link to Portfolio posts, Team posts, Product categories, etc. click on the “Screen options” in the right top corner and select the link categories that you need.
For more information, check https://en.support.wordpress.com/menus/