Reattaching fork to mountain bike - What is the correct assembly order?
There are a number of different schemes for fork headsets, but this seems pretty close to what you have:



Here is a different image of an older design, but with the same basic components, and a little easier to understand.  What's called the "crown race" in the first image is called the "bottom cone" in the second.



And this link may help you understand things a bit better.