Scalar :- Scalars could be a string, a number a simple variable or a reference. A dollar sign ($) is the scalar precedent.
Arrays :- It’s an ORDEREDLIST of scalars, which is accessible by numeric index as it is an index, so it's supposed to START with zero (0). @ is the preceded sign for arrays.
Hashes :- Hashes are unordered sets of key or value that would be accessible by USING the key as subscripts. A percentile (%) sign is the precedent.