I want my domestic shipping to be free over a certain amount, how do I set that up?

Start by looking at your shipping settings, on the far right side of the blue bar click on the gear-shaped button and go to Settings > Website Settings > Shipping, and click to Configure your shipping methods. Check the box for the method you want to work with and click to Edit. Scroll down until you see the table with your From and To numbers and the Rates. Look at your bottom-most line: the 'To' amount in that line should be .01 less than the target amount over which you want orders to have free shipping. For example, if you want to offer free shipping to all orders $50 or over, your current bottom-most line would need to have 49.99 in the To column. Then you would create another rate line below that and you would have 50.00 in the From column and in the To column, you would have 'and up'. Then in the Rate column you would enter 0.00. Be sure to click Save at the bottom after you're finished adjusting your rates.