What's the meaning of this word. I'm so confuse with the word " 真的假的”

I think you heard from a Taiwanese,haha!
In Taiwan,it's a very common pharse,and it's just the same like 真的嗎? Really?
Next time,talk to your Taiwanese friends,you're highly likely to hear it.

你听到的那个消息是真的假的？

I think Chinese people use it to express their surpise, or doubt on something that they might have hard time believing in.

often used as a short answer in a dialogue. To express surprise and/or doubt in what the other person said

It depends on the specific context. In different contexts, the meaning to be expressed is different.
For example:你说的是真的假的? Indicates that it is true or false.
我简直不敢相信，真的假的? Expressing surprise, wanting to confirm.
不会吧，真的假的? Doubt that it is not true.