All about proportions.
If you do so many miles in 12 mins, then how many miles in 60 mins?
Lets say you did 24 miles. 24/12 = ?/60
Simple maths or whiz wheel can help you there.
If you use a similar logic with all time, distance, speed calculations you might find it easier.
One on one with an instructor should sort out any confusion. If it doesn't, your instructor is no good at his/her job and you should seek one that can explain your query so that you fully understand the concepts. Don't go home confused.