Hi,
Well, if you just want to always provide a "free shipping" shipping method, then just create a new shipping method of the type "manual" via the System>Shipping methods with a price of 0 and the name "free shipping".
Then, your customers will be able to select it on the checkout.
If you want to offer the free shipping only above a certain amount, enter that amount in the "minimum price" setting of that shipping method and enter the amount minus 1 cent in the "maximum price" setting of the other shipping methods you have (or maybe not if you want to keep the other shipping methods available).
Beware of the "include virtual products price" setting of your shipping methods to take into account products without a weight (or not).
