The phrase "How do you do?" in English is a formal greeting typically used when meeting someone for the first time. In German, the equivalent formal greeting is "Guten Tag!" or "Wie geht's?" (meaning "Good day!" or "How are you?"). When introduced, Germans often say "Freut mich, Sie kennenzulernen" which means "Nice to meet you".

If looking for a direct translation of "How do you do?" as a polite greeting, "Guten Tag!" or simply repeating "How do you do?" (as it is idiomatic in English) is common. The response to "How do you do?" in German is typically the same phrase or a polite "Guten Tag".

For expressions like "I do" in the context of affirming something (e.g., in marriage vows or agreeing to do something), the phrase commonly used in German is "Ich will" (meaning "I will" or "I do" as a vow) especially in a wedding context. More generally, Germans answer affirmatively with "Ja, habe ich" (Yes, I have) or just "Ich" (I do) depending on context.

In summary:

• "How do you do?" as a greeting in German is "Guten Tag!" or "Wie geht's?"
• "I do" (as in agreeing or affirming) can be "Ich will" in vows or "Ja, habe ich"/"Ich" for general affirmative answers.

This covers the usage and translation nuances for "how do you do" and "I do" in German.