Not able to get a decent score with daily workout when interval training

I really don't know why but any time I have an interval training I get a lousy score... like 0%.

Actually I really am confused: first sometimes it says (on watch and spoken) 20 seconds but then it makes 3 beeps only after 10 seconds. 

Then it says rest 15 seconds so I wait that time and nothing happens....

I mean should it be intuitive or am I supposed to follow a tutorial to understand?

Thanks