@mmangiamusardo please mark your post as having spoiler content next time.

.Length returns the total length of the string starting from 1. We need to access the index which begins at 0. If we wanted to access the last index of the original string it would be Length-1. Since we want to cut the last character off, we use -2. Hope that helps

The first character is the other of the two.

The solution is taking a substring starting from the second character and a number of charachers after that equal to the length of the full string minus two.

Example:

12345

You want 234, which is three characters long. You tell it to skip the first character and then take the three characters after the first one. Therefore it is the length of the full string minus two.