This indicator plots labels that indicate gaps whenever the open price and the previous bar close price have a significant gap.
To determine the size the gap has to be before it is labeled at a specific point in time on the chart. The gap needs to be larger or equal to a factor of an ATR value. For example, if the ATR gap factor is 0.25, the gap between the open and the previous close price must be greater than 0.25*ATR of the ATR length specified for the gap to be plotted on the chart.
Note: If you don't know what the ATR or average true range is, search for "ATR" in indicators. It is one of Trading View's most fundamental indicators.