What does D3, D2, D1, mean in Automatic cars?

I've owned only Manual transmission cars all my life; just got my first automatic. I know the first D puts you in Drive, but what does D3, D2, D1 really do or mean. I know it has to do with weather condition and hill climbing or something. Please advise. I'm just hoping to get answer from you guys before... show more I've owned only Manual transmission cars all my life; just got my first automatic. I know the first D puts you in Drive, but what does D3, D2, D1 really do or mean. I know it has to do with weather condition and hill climbing or something. Please advise. I'm just hoping to get answer from you guys before actually sitting down and read the literature
And for those of us that just reads and gives nothing but harsh responses, please stir clear and don't waste your time.

Respectfully submitted.
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