All shops must set their shipping for their full shop via:
Shop Manager > Settings > Shipping
You simply add the charges for National (UK) or International shipping and then add the fee you wish to charge for shipping.
Here you can also set maximum shipping costs to ensure that the shipping cost is not charged on each product purchased.
This will set the shipping costs for your shop overall.
If your products have different shipping costs you can add shipping on the edit/add product form.
Please note: Shop shipping must be set for customers to be able to buy your products, simply having it at product level will not work.