。
I quit smoking a year ago.
Literal
I [topic-は] one-year before [at-に] quit-smoking-did.
禁煙する (きんえん, 'to quit smoking') — 禁 ('prohibit') + 煙 ('smoke'). 一年前に ('one year ago') — time expression with に. A simple factual statement.
。
I quit smoking a year ago.