If the Relative Performance indicator is rising that means the selected security is outperforming the CNX500 index, and vice versa if the indicator is falling.
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.