Well, if you do copy the code you've just posted, it won't run and will give an error message because you missed giving the counter "i" a name in your loop.
for ( int = 10; i > 0; i--) --> int i, not just int
Ok. What's happening in the loop is that i is going to decrement by 1 as long as it's greater than 0 and then be multiplied by 2.
1st iteration: i = 10 and 10 > 0 --->> output: 10*2 = 20
2st iteration: i = 9 and 9 > 0 --->> output: 9*2 = 18
it will keep going until the condition is met in your loop. That'll be the 10th iteration when the condition is met.
10th iteration: ---->> output: 1*2 = 2
I hope this helps you with understanding for-loops.. They can be quite tricky!