对/给
duì / gěi
对 turns your face; 给 puts something in a hand
The picture 对 is your body turning to face someone. 给 is something leaving your hand and arriving in theirs. With 对, nothing changes hands. 跟我说 is talk you and I trade sitting face to face; 对我说 is speech thrown one way, at me. 跟 has an exchange in it; 对 has only a direction.
Where the picture shows up in 对/给
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the way your face is turned
他对我笑了笑。
tā duì wǒ xiào le xiào
He gave me a little smile.
Turning your head toward the person opposite, catching their eye, and letting the corners of your mouth lift
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what an effect lands on
抽烟对身体不好。
chōuyān duì shēntǐ bù hǎo
Smoking is bad for your health.
A no-smoking poster where the smoke runs like an arrow straight into the figure's chest
Good for, bad for, about — all of those are always 对.
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putting it in someone's hand
请给我一张收据。
qǐng gěi wǒ yì zhāng shōujù
Could I have a receipt, please.
A receipt passing over the counter and landing on the other person's open palm
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sending words across
我一会儿给你打电话。
wǒ yíhuìr gěi nǐ dǎ diànhuà
I'll give you a call in a bit.
Picking up the phone, tapping their number, and sending your voice across to their end
Things that reach a person — 打电话, 发信息 — take 给. 对你打电话 is wrong.
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setting it aside as their share
我给你留了一份饭。
wǒ gěi nǐ liú le yí fèn fàn
I saved a plate of food for you.
A covered bowl of rice set aside at the table and pushed over in front of their seat
All of it in one picture
The little smile turns your body toward someone — that is 对 — and smoking being bad for you is an effect landing on a target, 对 again. The receipt changing hands is 给, the phone call is your voice crossing over, also 给, and the saved plate is a portion set aside as their share, 给 once more. The line runs in one place only: direction alone takes 对, and something actually crossing takes 给.