Answer 1

hashes are a ONE-way encryption which means you cant get the original back. It is also important that you have a low collision rate of two objects (they have the same hash). Hashes are very usefull in saving passwords or detecting changes of a file object ect because if the file, object or entered password has not the same hash which is in the database you know it is the wrong password without saving the real password or you know someone has tempered with important files. also in some coding languages we have a hash table / list where you save the object at the index of its hash this shortens the searchtime of this object.