As far as I know, Tinderbox has the very basic Apple Text Engine behaviour for bullets: i.e. you have to invoke the first bullet / number from the Lists dropdown box (or in a slightly different form from Format > Text > List...).
NB: the Lists dropdown box is only available if you've got the Ruler showing (Format > Text > Show Ruler (Ctl-cmd-R)).
Once you've started the list off, then it will continue to indent automatically as you press Enter at the end of each list point.
BTW, you'll probably find that the list and bullets feature is a bit clunky -- that's Apple's fault. People have been asking them to improve it for years, but bullets (and tables) remain as irritating to use as ever.
You can avoid some of the irritation in most programs based on Apple Text (Scrivener, Devonthink, TextEdit etc) because you can press opt-tab and it will begin a bullet point (-) list.
Unfortunately it's hardwired into the Mac so you can't change the shortcut which means that you can't use it in Tinderbox, as the latter has opt-tab as 'move the cursor between outline and text panel'. Sadly, this command isn't on a menu so it's not possible to remap it.
The upshot is that the only way to get automatic bullet points in Tinderbox is to use the Lists dropdown box.