Tinctures work primarily through sublingual absorption through the tissue in the mouth.
You'll find most use ethanol, be prepared, the higher proof the ethanol, the more the tincture is likely to burn, so be prepared to dilute. There are some tinctures that use glycerin, which doesn't have the burn problem of the alcohol, but generally also aren't as potent.
Tinctures you want to swish around in your mouth, hold under your tongue for a 15-30 seconds (approx), then you can swallow, whatever isn't absorbed sublingually will be digested and processed by the liver for a little delayed action.
Edible oils, extracting from flowers or adding concentrate, easy to make, as long as your digestion works and you can process edibles (some folks can't)... folks use them sublingually as well, but more happens after digesting what you swallow what you take.
Tinctures generally use a number of drops or an entire dropper.
Your question about using it in the bath, like a bath salt? You could, I'm not sure how that would work... never had good results topically.
Making concentrate (which is what's required for vape pens, regardless of size) is a more involved process, easier if you have the right equipment (there's a thread on FC about 'The Source', check that out).
@TomBstoned is your base alcohol or glycerin? not sure how MCT would blend with either.