Hi Geetha,
You have many SAP help documents on this basic requirement.
Cost Center is a Cost object helps to track the cost. We can create Cost Center for a division, department, location, product and regions.
Whereas COPA (Profitability Analysis) is a one of CO - sub module helps to get the profitability of your entity. You can get the profitability with a combination of a product, customer and region. i.e. Knowing the profitability of a product with respect to a particular customer in a particular region.
BR, Srinivas Salpala