Explanation

A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z.

ANPL 

BOOK 

the next alphabet of A is B, N is O,

the before alphabet of P is O, K is L

so 

GZOE 

HAND 

the next alphabet of G is H, Z is A

the before alphabet of N is O, D is E