Nucleus Card's can be set to directly link to an external URL and this URL can be customized within your Page Settings.
To access Page Settings, select the page you want to edit and scroll down to the settings section of that page.
Upon switching on the option to enable the page to redirect to a URL, you'll notice a new set of options appears.. Here, you can begin customizing your Card's external linking URL. Paste the external URL you wish to directly link your card to into the field provided.
If you wish to have your Card link open within a new tab in a user's browser, make sure to select the checkbox option to allow for that. Leaving this box un-checked will mean your Card link will open within a user's existing Nucleus tab.
When you're ready to to update your Page and commit these changes, click the 'Save Changes' button at the bottom of the page.