thanks a lot. All answers are quiet useful.
So tips is in early stage I should keep it myself or cut it into parts. Only after I have done some work on it should I start to talk to someone else about it.

So the next question is: Is the advisor also one of "someone else"?

I am a fresh phd student. I am comfused about how should I talk about my ideas with colleges? I mean in early stage, if I told a college my idea about one project, there is the risk that, he may realise the idea and get a paper published. But I will not get the credit because I am a fresh phd and I am not so familiar with that field, so end up do not contribut too much to realise that idea. But still I got the idea!

So what do you guys do in this situation? If you get a idea in some field you are not very familiar with, will you talk about the idea with a more senior college in that field?