Click-Through Rate (CTR):
Generally, the email click rate is the percentage of contacts who click on a link within an email. This is also called the email click-through rate. The main goal for tracking the click-through rate is to measure the engagement of the recipients. 
This is calculated using the below formula 

Click rate=Emails clicked / (Email sent - Bounced)

You may optimize your CTR by adding relevant images and CTA buttons which will improve the engagement of the audience. 

Click to Open Rate (CTOR):
The click-to-open rate compares the number of unique clicks to unique opens, in simple terms it is the number of clicks out of the number of opens. This gives you a better measure of how the email design and the content pulsate with your targeted audience since these clicks are captured from the contact that actually viewed your email, unlike click-through rate. It is calculated using the below formula,

Click to open rate= (Total email click/Total email opens) *100

Essentially, the click rate takes into account all of the inbox actions. But on the other hand, the click to open rate only includes the actions of those who have opened the email.