Brought is the past tense and past participle of the verb bring. If you say ‘He brought his dog’, you mean that he has his dog with him when he came.
1. My secretary brought my mail to the house.
2. He was glad someone had brought a camera.
Bought is the past tense and past participle of the verb buy. If you say ‘She bought a newspaper’, you mean she obtained a newspaper by paying money for it.
3. I bought myself a piece of chocolate cake.
4. She bought a piano.