The green line represents the 20 weeks and the red line represents the 21 weeks . The best way to read the current value is to look at the weekly chart, but any time frame will display the same values.
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.