Let's start from the simpler example:
int first =
int second =
int result = first > second ? first * 2 : second * second;
The last line is
strictly equivalent to
int result;
if (first > second)
result = first * 2;
else
result = second * second;
Using this idea, you can understand your example, where the same feature is used in a nested way: two expressions in round brackets are the branches or first '?' operator and use '?' themselves.
—SA