Let us say we have a series of letters
A, B, C, D, E, F, G, H
Which one is
1) the first letter from last
2) the second letter from last
3) the first letter before last
4) the second letter before last
5) the second-last letter
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
In the list you gave, "G" is the next-to-last, second-to-last or penultimate letter.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.