be good at 擅长; 精通

【例句】

You must be good at learning at first.
你必须首先擅长学习。

Given that each person can be good at different things, you can expand your scope of knowledge by making different friends.
由于朋友擅长各个不同的领域，那么，你将可以通过结识不同的朋友来扩展自己的知识面。