If you click on the line it will color the bars of the chart based on if they are above or below the - This is just visually helpful for me to see the active trend.
Make sure you hover over or click on the line to see the colors of the candles change - it's not visible by default or without doing this.
Thanks to @pacbrother for catching this.
I still don't recommend you use this at your only alert to enter or exit a trade. I just use this as a visual confirmation with other indicators.
Check out this video:
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.