Thanks Michael for reply.
The decode function acts like this

select emp_id,emp_name, sex from emp

emp_id emp_name sex
------ -------- ---
001 John M
002 Susie F
003 David M
004 Dummy null

Using decode

Select emp_id , emp_name , DECODE(sex,'M','Male','F','Female','Male') SEX
From emp

emp_id emp_name SEX
------ -------- ------
001 John Male
002 Susie Female
003 David Male
004 Dummy Male

Thus the format is as below

DECODE(value,if1,then1,if2,then2,.......else)

TIA