verb; seize state power; conquer the country; open up (a career or business)
Definitions (粵典–words.hk)
動詞
去佂服敵人，接管領地，建立國家，現引申為發展事業。 to conquer and defeat the enemy in order to build an empire, now usually refer to development of business or career.
成吉思汗好年輕就開始打天下，慢慢建立蒙古帝國。
成吉思汗好年轻就开始打天下，慢慢建立蒙古帝国。
Genghis Khan started to build the Mongolian Empire by conquering enemy and taking over lands when he was young.
芬姨一畢業出來做嘢，第一份工就係同佢老闆去中國打天下，為公司發展中國業務。
芬姨一毕业出来做嘢，第一份工就系同佢老板去中国打天下，为公司发展中国业务。
The first job of Aunt Freda right after she graduat was to set up new business in China for her employer.
Definitions (Kaifangcidian)
（沒有對應漢語詞彙）
Examples (粵典–words.hk)
Cantonese
成吉思汗好年轻就开始打天下，慢慢建立蒙古帝国。
成吉思汗好年輕就開始打天下，慢慢建立蒙古帝國。
Genghis Khan started to build the Mongolian Empire by conquering enemy and taking over lands when he was young.