This indicator plots a line that shows the high and low of a higher time frame than the one where you have actually in your chart. For example if you want to see the high and low of the day while you are in 1hour chart, set Boundaries to Daily.
Boundaries have predefined Monthly, Weekly, Daily and Hourly time frames, but if you want to use a different timeframe, just choose the option Other_TF and write on the next field the minutes for your desired timeframe. As MT4 only works beyond M1 with 5, 15, 30, and 240 minutes timeframes please only use them in the Other_TF option.
Boundaries is only shown in time frames lower than the specified in it's properties. In the Colors tab you can set the color for the up boundary and down boundary. Please watch the video to get better understanding of how this indicator works.