The Tagging Window is where you tag your custom instruments with their various categories before generating the part for Soundpaint.
To open the Tagging Window, click "Tagging Window" from the Window drop-down menu at the top of the Soundpaint Editor
It is especially important to tag the “instrument” category, because that determines where the part is shown in Soundpaint. If no instrument is tagged, the part is going to show up as “unclassified” in Soundpaint.