Free Shipping Bar tells each shopper how much is left to add before shipping is free: "Add $12.50 more for free shipping". The amount comes from that shopper's own cart and changes as soon as they add or remove an item.
Type your free shipping amount once, the same one you set in your shipping rules. Before anything is in the cart the bar says "Free shipping on orders over $50". When the cart passes the amount, the bar fills and the line changes to "You get free shipping on this order". Digital downloads and gift cards don't count toward the goal, and shoppers who pay in another currency see the amount in their currency.
You can rewrite all three messages, pick the bar colour and font, add a "View cart" link, and place the bar on any page. The editor shows a sample cart, so you see the filled bar before any order comes in.
The free plan has one goal with your own messages and a small credit link under the bar. Premium adds a second goal, such as a free gift above $100, start and end dates for a holiday offer, hides the bar while the cart is empty, adds a full-width strip style and your own background and text colours, and removes the credit link.