If FINE is coded as IFFI, …

FINE:
Skip 1 letter from F and write next letter: I
Skip 2 letters from I and write next letter: F
Skip 3 letters from F and write next letter: F
Skip 4 letters from F and write next letter: I
So FINE is coded as IFFI.

Next TASTE:
Skip 1 letter from T and write next letter: A
Skip 2 letters From A and write next letter: E
Skip 3 letters from E and write next letter: T
Skip 4 letters from T and write next letter: T
Skip 5 letters from T and write next letter: E
So, TASTE is coded as AETTE.

Similarly, TEACHER:
Skip 1 letter from T and write E
Skip 2 letters from E and write H
Skip 3 letters from H and write E
Skip 4 letters from E and write R
Skip 5 letters from R and write E
Skip 6 letters from E and write E
Skip 7 letters from E and write R
So, TEACHER is coded as EHEREER.