It is easy to move items from one library to another. When two or more documents are open, the top of the Library will show a drop-down list of document names. Select the library that holds the items you would like to take. The Library panel will now be available to use. Drag from the Library to the stage of the new document and the item will automatically be added to the stage and library of the new document - even if you delete the instance from the stage of the new document, the library will still retain the item.
You may also open the library of another document by selecting File > Import > Open External Library.
The symbol will be copied from one file to another, but it will not remain connected to the original. There are two ways for a symbol to remain connected to the original. Neither is covered in this course. But, one technique is called Runtime Sharing. Runtime Sharing means that the symbol is updated every time you run the .swf - after it is published. You may also set the Source of a symbol. This method executes before the file is published. Both of these are set in the Symbol's Advanced Properties window.