I mean he's been missing for several days. 我是说他失踪好几天了。

　　I mean I've been losing weight these days. 我是说这两天瘦了不少。

　　I mean today, not tomorrow. 我是说今天，不是明天。

　　I don't understand what you've saying.  我不明白你在说什么。

　　I mean I want you to help me.  我是说，我希望你能帮我。