“于”是一个书面语里常用的字，意思很像“在”或者“到”。

"于" is a commonly used character in written language, meaning something like "at" or "to".

我们说话时不太用它，但在书本和正式的文章里常常看到，比如“生于中国”。

We don't use "于" much in speech, but it often appears in books and formal writing, such as in "生于中国".