If you want to copy some of your items into another collection, you can do that using the bulk edit toolbar.
Start by highlighting the items that you want to copy by hovering over the items and clicking the tick mark that appears in the top left corner. Once you have selected the items you wish to copy, select ‘copy’ from the toolbar at the top of the screen. A window will ask which collection you want to copy the items into, select or type the collection’s name into the textbox and click ‘copy’. Your items will now be copied into the second collection!
Note: The collection that you are copying to needs to exist before for you can copy items into it successfully.