Your site’s conversion rate is the number of times a user completes a goal divided by your site traffic. If a user can convert in each visit (such as by buying a product), divide the number of conversions by the number of sessions (the number of unique times a user came to your site). If you sell a subscription, divide the number of conversions by the number of users.
Conversion rate optimization happens after the visit makes it to your site. This is different from conversion optimization for SEO or paid ads which focuses on who clicks through to your site from the organic search results, how many clicks you get, and which keywords are driving traffic.