Which of these sentences is correct? Why?
You must hear to this song.
You must listen to this song.
Have you heard to this song?
Have you listened to this song?
Either is correct, but they have a slightly different emphasis in their meaning. Hear is generally regarded as a passive activity, something that happens whether one wants it to or not. Listen, on the other hand, is regarded as an active activity requiring the participation of the user.
I might say the following:
If the person heard the song, and was unimpressed, I might then reply:
As reported in another recent question, listen is an intransitive verb and does not take a direct object; you must use a prepositional phrase to specify the thing being perceived. Hear, on the other hand, is transitive and can take an object, so you can say:
In the sentences you reported, you can use either hear or listen.
Generally speaking, listen and hear have similar meaning; two of the meanings of hear are listen, pay attention.
In specific contexts, listen is used instead of hear; for example, when a sentence uses the imperative mood, listen is used.