When we fill someone in on something we bring them up to date.

当我们向别人介绍某件事情时，我们是向他们介绍最新的情况。

To fill someone in is to give them information.

填写某人就是向他们提供信息。

You can " fill someone in on your life" – give them the details, the information about your life that the other person might want.

你可以“让某人了解你的生活”——向他们提供对方可能想要的细节，关于你生活的信息。