On calling an HTML Export (via the File menu, or shortcut) a OS-style folder selection dialog is shown - select an existing folder or create a new one. The selected folder is the location to which export will occur. This location is remembered in the TBX so it should not normally be required to reset it after first use unless deliberately choosing a new location.
Depending on the size and complexity of your TBX, there may appear to be some delay before the dialog opens. This is because before doing a full HTML export, all agents are updated to ensure output is correct, especially where automatic updating of agents is turned off.
Once export starts the illustrated dialog appears showing the note currently exported. The total number of records being exported is also displayed above the name of the file currently being generated (the latter normally update to rapidly to be easily readable).
Once export starts a dialog appears showing the progress of the export process.
WARNING: Tinderbox does not seem to detect if you've changed the template but not the note - e.g. you're re-exporting to fix a template coding issue. In such a scenario you should delete the originals otherwise you'll see the export progress bar but the existing file is not being overwritten. At note level, in HTML view this can be fixed by clicking the 'Update HTML' button.
NOTE: using the Export button on a note's HTML view exports only that note's page - aliases and children of the note aren't exported. You must use a full export to ensure the latter are generated.