When you select folders or files to rename SongKong tries to guess what part of the folder path contains metadata such as artist name or album name and which part does not contain metadata. It then splits the folder path into Base Folder and Sub Folder, the reason for this split is that if your songs are renamed from metadata only the Sub Folder part is renamed by applying your rename mask to your metadata. If you specify a Move Folder or Unmatched Folder on the Move Files tab then the Base Folder is replaced by the Move (Un)Matched Folder
But its not always easy for SongKong to get this right so you can use the arrow keys to modify where the split is. Or perhaps you would like the whole path to be modified by the rename mask , in this case use the right arrow to put the folder path in the sub folder field.
For example:if your folder name was /Music/The Beatles/Revolver then usually the Base Folder should be set to /Music and Sub Folder set to /The Beatles/Revolver.