Answer: Based on your description I am not certain if your plant is Brugmansia (trumpets dangle downward, grows very tall with a tree-like form, usually grown as a container plant and brought indoors each winter) or Datura (trumpets face up, grows more like a bush, grown as an annual, often self seeds in the garden).
Brugmansia is a tropical plant and the seeds need heat to germinate and grow. If this is what you have, wait until next spring to germinate the seeds indoors. Soak overnight in water, then peel off the "corky" outer layer. Plant the seed in barely damp seed starter mix with bottom heat (soil temperature of 80 degrees is ideal.) It can take 2 to 8 weeks or longer to germinate. Repot seedlings as needed and plant them out after all danger of frost has passed and the weather is reliably warm.
If your plant is Datura, the seeds can be started as above (no peeling needed) or can be planted in the garden after frost.
Good luck with your seeds!
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