Your navigation is the top bar that you see on your website. It has your main links. Here is how to update those.
From your dashboard click "Menus"
You will see a list that contains the menus on your site. The two mains ones are "Main Menu" and "Footer Menu".
The Main Menu is the one at the top of your site.
The Footer one sits at the very bottom of your site.
Adding New Links
You can add as many links as you'd like to these menus. On the left, is a list of every pages on your website.
Check the box next to the page you want to add and then click the "Add to Menu" button.
Adding Custom URLS
Use the "Custom Links" option on the left to enter your URL and then click "Add to Menu"
Reordering Menu Items
You can reorder the menus by dragging and dropping the items on the right into any order.
Creating Submenu Items
If you'd like submenus under other items in the list, you can drag the item under another item and it will become a submenu. Drag it slightly to the right for this to happen.
Saving your menu
Be sure to click Save Menu at the top right before leaving the page.