This program I guess is a basic HelloWorld in a PL/SQL Block.
There is an extra space between the variable message and it's datatype varchar. Just remove it.
And also, while assigning the values, there mustn't be a space between a colon equal to(:=) and the single quotes(''). [It would work :) ]. For eg. in a PL/SQL block we use single quotes('') to declare a string.
Well I am new here. I don't know how Stack Overflow exactly works for a novice like me, but yes some gentlemen or lady has already commented about using the below command:
set serveroutput on;
Which is absolutely correct as far as my knowledge. It is necessary for executing PL/SQL Programs.
P.s. Do tell me if I am wrong anywhere. I am open to suggestions.