It works by turning the change in the fed funds rate into a user defined percentage (using a multiplier, by default a 1% rate of change implies a 10% change in the chart) and then drawing a box that distance away depending on the direction of the rate of change.
The size of the multiplier should depend on the duration of the asset which this is being applied to, for example, a long duration asset such as a high beta growth stock should use a larger multiplier.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.