A Swing Low is the low of the candle that has a higher low on either side. A Swing High is the high of the candle that has a lower high on either side.
In the case of Swing High, the high of the neighbour candles are lower than the high of the main candle itself.
In the case of Swing Low, the low of the neighbour candles are higher than the low of the main candle itself.
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.
It will be good to see that a candle swept/raided a previous swing high/low marked by your indicator.
I am looking forward to this possible upcoming update.