Bascially: ID3 tags are data about the files, that are embedded in the files themselves. Typically, artist, album, genre, year, title, and track no. Many audio players organize and play files using that information, not the files’ folder and file names. And so even if your folder and file names are in great order, if the ID3 tags are not, the files will play “out of order.”
You can add/edit the ID3 tags using freeware such as MP3Tag. With Windows, you also can right click on a file and get to the ID3 tag info. under one of the Properties screen tabs (a more cumbersome process, for more than a few files).
Again, though, and nicely, the Clip+ will use the files’ folder and file names to organize the files if you put the files in the Clip+'s Audiobooks folder (typically done in a sub-folder with the name of the audiobook). But, of course, if the file name info. is incorrect or incomplete (such as, the file names do not start with a track number so that they can be organized in numerical order–just like on your computer), the files will be organized and play “incorrectly.”
The way people tend to organize audiobooks by folder and file name, within the Audiobooks folder:
folder name: Harry Potter and the Sorcerer’s Stone
I hope that helps. You also can do a search here (box at upper left) for more info., on terms such as ID3, MP3Tag, audiobooks, etc.