This is the 528th most frequent Korean word.
구매
Purchase.
Here, '구매' is a verb derived from its noun form, used to describe the act of buying something as an accomplishment.
저는 새 책을 구매했어요.
I purchased a new book.
Here, '구매' is used as a noun to generically describe the concept of making a purchase online.
온라인 구매는 정말 편리합니다.
Online purchasing is really convenient.
In this sentence, '구매' functions as a noun, referring to the act of buying/sales transactions conducted by individuals.