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Questions & Answers about Wann kaufst du ein?
Why is ein at the very end of the sentence?
The verb here is einkaufen (to shop), which is a separable verb. In a German main clause or a question, the core part of the verb (kaufst) stays in its normal position, but the prefix (ein) is separated and pushed to the very end.
What is the difference between kaufst and kaufst ... ein?
The base verb kaufen just means "to buy" (usually a specific item, like a car or a book). The separable verb einkaufen means "to shop" or "to go grocery shopping". You need the ein at the end so people know you are talking about shopping in general!
Why is the verb right next to Wann?
In German questions that start with a question word (like Wann, meaning "when"), the conjugated verb must always take the second position. So kaufst comes immediately after the question word, followed by the subject du.
How do I know how to conjugate a separable verb like einkaufen?
You only conjugate the core part of the verb, which is kaufen in this case. Since the subject is du (you), you drop the -en and add the standard -st ending to get kaufst. The separated prefix ein never changes its form.