A conversion takes place when a visitor to your site takes an action you care about and “converts” to a customer. Track when a customer completes an action on your website. This could be, for example, making a purchase, signing up for a newsletter, clicking a button, or any other valuable action a customer can take on your website.
Goodle Destination Goal- Ecommerce transactions
To track transactions, you'll need to add Ecommerce tracking code to your shopping cart. This allows Google Analytics to calculate the Revenue and ROI metrics from purchases on your site. However, it's often useful to also create a destination goal to signal the completion of an ecommerce transaction. Setting up a destination goal will allow you to see the percentage of sessions that resulted in at least one transaction (i.e., this will be the conversion rate for that goal).