about "Einkaufen"
In this sentence"Möchtest du zum Einkaufen?"
What does this "zum Einkaufen"mean? Does "einkaufen" here change to be a noun? Why?

Question

Answer

When there is an article before verbs, this is called 'Nominalisierung' (becoming a noun). Zum is 'zu dem', therefore 'Einkaufen' is capitalized. 
Link: https://www.studienkreis.de/deutsch/substantivierungen-verben-adjektive-regeln-uebungen/
Meaning of the sentence: Do you want to go shopping?
You could as well say: Möchtest du einkaufen gehen? In this case it is used as a normal verb.

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