How to classify "unknown artist", "unknown album" in Itunes?
You want to re-import those songs into your iTunes library. When viewing the songs, sort by the date added field. (You can add columns by right clicking any information header in the song list and adding check marks to the menu that shows).

Since the exact steps vary based on your OS and the version of iTunes, you can add that to your question or use iTunes help on importing songs from the computer folders and it will show you how to add those missing songs to the Library database that iTunes maintains.

Once you have an imported song, you can use iTunes to add titles and albums so that the storage on your filesystem is proper.