To add a new navigation menu bar layer to your email design, you can click on any Column or Hero layer, then select the Navigation Links option from the Quick Add dropdown menu, then click the Add + button to insert the new nav bar layer into your layout, which includes a few placeholder navigation item links, too.

After styling the links to your liking, you can specify the clickable URL by clicking on any Link layer in Figma (nested inside of your Navigation Links layer), then clicking the Settings button, and pasting your URL into the Clickable URL Link input field; this will ensure that your nav link opens up that URL in the browser when it's clicked.

You can also add more Link layers to by clicking on your new Navigation Links Figma layer that the plugin created, then selecting the Link option from the Quick Add drop down menu, and then clicking the Add + button to automatically add the layer into your Navigation Links element as a new link.