Yes, linking to external pages is possible and done through the administration area in your account. After logging in, please click "Settings" on the top and then "Pages & Menu" on the left.
Here, select "Create new page / new menu item" on the top right. One of the offered options allows links to external pages and is named the same.
To create this page, you have to enter the page title, the forwarding target and the URL name. The linked page is then available as a seperate menu point in your shop.
This is how the setup looks:
IMPORTANT! Please do not set a link to an external site as the starting page of your shop. This would cause anyone who visits your website to be forwarded directly to the linked page.