The Woo Checkout Payment Element is useful when building a one page checkout. It is the last thing logically in the flow of the checkout, as it is from a button in this Element users place the order.
So to use this Element, simply add it in your Checkout layout at the bottom of the design. The Element will pull the payment methods set up in WooCommerce > Settings > Payments. If you use the Checkout Tabs Element, this Element is unneccesary, as all of the other four Checkout Elements are integrated in that one.