Now that you have got the mandatory advices, let's see:

Apart from the missing semicolon at the end of this line, the statement is faulty because you define a hash "%hash" and assign to it a hash reference {}! In order to initialize an empty hash you can simply use my %hash; or my %hash=(); assigning to it an empty list.

This one is good, assigns to the element "ONE" of the hash %hash.

This one is less good, tries assigning to the element "TWO" of the hash reference $hash which is undefined.