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.