Why would you need to do this you ask? You just never know. For a real world example where this came in handy, see the following post: Hiding List Data from Unauthorised Users
In SharePoint Designer, on the site you list resides in, click on 'workflows' and choose list you want to copy from from the 'list workflow' drop down list. Once you have named the workflow saved it, click on the 'edit workflow' option, and choose 'Copy List Item' from the list of available actions.

Choose the option to copy the current item to the list you want to copy to, as per the screenshot below.
Next, go back to the settings page for that workflow and tick the 'start workflow automatically when an item is created' box.
Next save a publish your workflow.
Test the workflow by creating a new item in your first list. Next, go to your second list and check that the item has been copied across to this list.