I'm guessing the "unassigned" files are missing Album or Artist or both. The answer is the same either way. Highlight all the songs from the same artist and album (like the 3 from Rubber Soul). Open the Tagging Pane (right click and select Tag).
In the Tagging Pane on the left, find Album and Artist. Click in the box to the right of each field and use the pull down list arrow to find the correct Artist and/or Album. That should assign them correctly. Your changes should show in the Tagging Pane immediately. But you may need to refresh your view to see them move from unassigned to the proper album and artist views.
While you're at it, you might check the other fields that are important to you. Things like track #, Date, Genre, etc.
Good luck.
Brian.
