There are three steps for a successful signup, first is when a user submits a form, second is when a user open the confirmation link and third is when the user registers.
Goals can be tracked by two ways, either by destination url or setting up events on successful signups.
Read this for setting up goals using destination url
https://marketlytics.com/analytics-faq/setting-custom-goals-google-analytics
And this for setting up events on successful signups.
https://developers.google.com/analytics/devguides/collection/analyticsjs/events
