@zjv5002,

于 is a preposition. One usage is almost the same as 在, but more formal and a lot older. It's usually used in chengyu or old set phrase, like 生于中国 (born in China). That's why you don't often see it in the daily life.

Other common usages of 于 are: a) towards, like 求救于人 (asking help from people); b) to, like 献身于科学 (dedicate oneself to science); c) from, like 青出于蓝 (the disciple outdoes the master; d) this last one is the most useful in modern times: to compare, like 大于，高于 (bigger, higher).

--Echo

echo@popupchinese.com