A flat rate shipping for all orders can be added to the product catalog. Shipping will be added to the cart when items are added.

For flat shipping, configure the product catalog block used for checkout and set a value other than $0 for the Handling charge per order and select "Flat" as the Shipment Charge Calculation.

This charge will appear as "Shipping" in the cart's subtotals.

Free shipping is also an option in promotions. When a promotion establishes free shipping the flat shipping charge will fall to $0 and there will be no shipping line in the cart's subtotal.

Note: FreeShipping is not always the best deal.  A buy 2 get 1 free but pay shipping, for example, will typically be a lower price than just free shipping, so if you still see a shipping charge use Explain Promos to see another promotion with a lower price was used.