On the main products page, you can see Copy, Paste and Clone icons.
These actions can be performed with more than one product with the help of Products toolbar (see picture above) or products context menu:
First, you have to copy selected product and go to the category you need. When you're pasting the product, you're creating the new one with the new ID.
Clone Products option is actually like a combination of copy and paste buttons. It will copy selected product and place it in the same category with the new ID number and the post-fix "- clone" at the product's name.
This way is easier and faster than copy/paste.
The video tutorial below shows the basic principles of pasting, copying and cloning products in Store Manager clearly.