Explanation :

S $\xrightarrow{-1}$ R            L $\xrightarrow{-1}$ M
H $\xrightarrow{-2}$ F            K $\xrightarrow{-2}$ M
I  $\xrightarrow{-3}$ F            U $\xrightarrow{-3}$ X
F $\xrightarrow{-4}$ B            M $\xrightarrow{-4}$ Q
T $\xrightarrow{-5}$ O            B $\xrightarrow{-5}$ G

The first, second, third, fourth and fifth letters in the word are respectively one, two, three, four and five steps ahead of the corresponding letter of the code.

Explanation :

Clearly, the letters in the word ‘GOODNESS’ are moved alternately one step forward and one step backward to obtain the letters of the code.

G $\xrightarrow{+1}$ H$~~~$G $\xrightarrow{+1}$ H    
O $\xrightarrow{-1} $ N$~~~$R $\xrightarrow{-1}$ Q    
O $\xrightarrow{+1} $ P$~~~$E $\xrightarrow{+1}$ F    
D $\xrightarrow{-1} $ C$~~~$A $\xrightarrow{-1}$ Z    
N $\xrightarrow{+1} $ O$~~~$T $\xrightarrow{+1}$ U    
E $\xrightarrow{-1} $ D$~~~$N $\xrightarrow{-1}$ M    
S $\xrightarrow{+1} $ T$~~~$E $\xrightarrow{+1}$ F    
S $\xrightarrow{-1} $ R$~~~$S $\xrightarrow{-1}$ R    
                                $~~~$S $\xrightarrow{+1}$ T         

Explanation :

STEP 1:

GIGANTIC =>  GIGTANCI

There is 7 letters words.First three letter and second and last letters are same.6th letter takes 4th place,4th letter takes 5th place and 5th letter takes 6th place.Similarly

MIRACLES => MIRLACSE

Explanation :

STEP 1

Here +1 means one step forward and -1 means one step backward.Downward arrow means from upper to lower.

   G   A    M     B     L     E   

+1↓  -1↓  +1↓  -1↓  +1↓  -1↓ 

  F    B     L    C     K     F 

STEP 2

  F   L    O    W    E   R  

+1↓ -1↓ +1↓ -1↓ +1↓ -1↓

  E   M    N    X    D    S  

Explanation :

STEP 1

Here +1 means one step forward and -1 means one step backward.Downward arrow means from upper to lower.

   P    A     P     E     R      

+3↓  +2↓  +4↓  +2↓  +5↓ 

  S    C     T     G      W   

STEP 2

  M    O     T      H     E     R     

+3↓  +2↓ +4↓  +2↓  +5↓ +2↓ 

  P    Q     X     J      J     T