How does this scam/carding method work?

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I recently met someone who does alot of fraud, and he told me about some stuff but i am a complete beginner at carding and didn’t really understand what he was saying. He told me he would tell people to give him and empty debit card for one day and he would give them 100$ cash. How does he make money of off this? He told me something about spamming logs but im just interested in how he does this.​