Since there are a lot of ways how your files can be named, you will have to set the correct pattern in the "Format (arrow down)" control at the left of the button you mentioned. If the format is "%{artist} - %{album}/%{track} %{title}", then you will need files named like "01 First Title.mp3" in folders named like "An Artist - An Album". If this is not the case, you have to choose a format which matches your names. There are quite a few formats predefined in the combo box, but you can also add your own. Kid3 will also try to guess the format from an internal list of possible formats (if the given format does not match, see in the handbook for details), but usually, it is safer to explicitly adapt the format to match your file naming scheme.