。
My mother bought me that book.
Literal
Mother [topic-は] me [for-に] that book [object-を] bought-[benefactive-polite-てくれました]
買ってくれました combines 買う ('buy') with the benefactive auxiliary ~てくれる in polite past form. The benefactive frames the action as done for the speaker's benefit — the listener hears not just 'mother bought a book' but specifically 'mother bought a book for me.' The polite ~ました fits a context where the speaker is recounting this to someone outside the family.