It draw vertical lines on the chart. For example you can mark Longon and NY sessions open. Or just draw at every hour. Line color depends on swap rates. If swap rate for long is bigger the lines will be lime. If swap rate for short is bigger then red.
Also it draw Asian session High and Low at selected time. Default settings are: 3am – 10am is Asian session period to check. 3am – 5pm distance to draw lines. So ar 10am (London open) it will draw 2 lines: Asian High and Asian Low.