Answer:
It all depends on the model you are asking about. Crosman has made over 100 different models. So first you need to identify the model you are asking about. You can usually find the model number on the barrel.
Then I suggest that you go to ( see the Link Below) and locate your gun. The diagrams will help you re-assemble it.
Over the years CROSMAN has made over 50 different BB guns and more than 100 different Air rifles. It would really help if you stated which one you wanted help with.
Is this a BB gun or an Airsoft BB gun? If it's Airsoft then you are in the wrong category. There is an Airsoft category for Airsoft.