bought this bookこの本を買った is the past form meaning “bought this book.” In the example sentences, 買う also appears in other forms such as 買ってくれた (bought it for someone), 買いたい (want to buy), and 買いに行った (went to buy).
JA: 昨日、駅の近くでこの本を買った。
EN: I bought this book near the station yesterday.