If you have a ecommerce shop running you should have your transactions already set up as conversions in google analytics. But if you just have a blog or another business without direct website transactions you should definitely add secondary conversion goals for other actions.
These actions could be a newsletter subscription, or a form submission for a custom quote on a service you provide.
These goal conversions can be set up in your google analytics view settings.
A pretty easy set-up would be a form submission that has a specific thank-you page that you could define as a goal conversion.
More complicated goals are typically set up with events. You can set these events with Google Tag Manager and Auto-Event Tracking pretty easily. Check out this great article if that’s what you need to do for your specific case.