Bought | brought

Brought and bought are both the past simple and past participle forms of their respective (irregular) verbs, (← What does this mean? Rules for understanding irregular verbs in English.) and they sound very similar.

Bought

Bought comes from the verb buy - there is no r in buy, and so there is also none in bought.

In the past Russia bought New Zealand dairy products by exchanging them for Russian-made motor vehicles.

I had already bought the takeaways when I was told there would be no-one at home for dinner.

Idioms with buy:

There are some unusual things that you can buy (metaphorically) (or which don't mean actually using money). [To see the meaning of these uses of "buy" hover over or click the bold words below for a pop-up explanation.)
buy trouble | buy (more) time | buy a pup/dog/lemon | buy the farm

Brought is the past form of bring... and notice how bring has an r in it, and so does bring.

They haven't brought their lunch, but it's okay because we've got plenty to spare.

Each participant brought a unique skill that was needed by the group.