Could aliens use online shopping if they studied humans?

Yes—if they had studied humans well enough, aliens could probably use online shopping, at least in principle.

The exact difficulty depends on how advanced they are. A spacefaring species would likely be able to interact with human internet infrastructure, imitate normal browser behavior, and access online storefronts without much trouble. They might not even need a human-style bank account if they could use alternative methods such as cryptocurrency, gift cards, or other assets accepted in practice.

The bigger question would be logistics rather than browsing: how to pay, and how to receive physical items without revealing their location. For digital goods, that part is easy. For physical goods, they could potentially use pickup lockers, intermediaries, gig workers, shell companies, or other delivery arrangements.

So the short answer is yes: if aliens understood humans closely enough, online shopping would be very plausible for them.