I can try, I don't know how plain it will be...
Unique open rate - you have that exactly right.
Click to open rate - I think this is unclear. The phrase "click to open" is ambiguous, it sounds like it's talking about clicking in order to open up the email but that's not what it is. This is the proportion of opens that resulted in a click through one of the links in the email to actually visit the landing page (or whatever you're linking to).
The unique click to open rate is just the "unique" version of the click to open rate, that is, it is the proportion of individual people who opened the email that then actually went on to click through to the landing page.