Answer:
It is very simple.
Say we have a video game for $50, and you have a 10% off coupon. To able to find the discount, we have to take off the 10%. To do this, we can easily convert 10% to a decimal: 0.1. Remember though, for percentages they always have a denominator of 100. If there is something that's 200%, it would be 200/100 which is x2 greater. If something is 0.1%, it would still apply the same and it would be .1/100 or 1/1000.
Now back to the first problem. If we are going to take off 10%, we need to multiply $50 by 0.1 to get $5. To find the final price, we could subtract the original price by $5. So $50 - $5 = $45. I hope this helps, sorry if it was too complex but this was the easiest I could explain it.