表达 “know something back to front” 的意思是 “对某件事情了如指掌，或对某个话题有深入的了解”。

例句
You’re an expert in computing. You know computers back to front.
你是计算机学方面的专家。你对电脑了如指掌。

She is fluent in five languages. She knows English back to front.
她能流利地讲五种语言。她讲英语游刃有余。

That’s Jerry’s favourite game. He knows it back to front.
这是杰瑞最喜爱的游戏。他对其了如指掌。