Click-through rate is clicks divided by impressions: the share of people who saw the ad and clicked. Conversion rate is conversions divided by clicks: the share of visitors who did the thing that matters after landing. The two diagnose different problems. Weak CTR points at the ad; weak conversion rate points at the landing page or the offer.
Add ad spend and the 412 Freelancers calculator also returns cost per click and cost per acquisition from the same inputs, so one set of campaign numbers gives all four metrics at once.