To copy a product click on the "copy to" which you will find by clicking on the product in admin> Catalog & Products> Categories / Products.
With this feature, you can link or duplicate or link a product to a different category.
What is the difference between linking and duplicate?
When you link you retain the same product but you let it appear in other categories simultaneously. If you change your product (name, description or price, etc.) in one place it changes in all categories.
Stock availability is also linked.
When you duplicate a product, you create a copy of the same product to a new category. It then becomes a new stand-alone product. If you change something, it will change only for that product and category
(useful if you want to eg create a template to save time)