Horizontal lines help you to put Quarter Theory lines on your chart. It's defaults are meant for EURUSD , but you can change it for other charts. There are 16 lines in this indicator.
For EURUSD recommended settings right now are: Starting Price (Bottom):1.12 and Gap: 0.0025 USDCAD: Starting Price (Bottom):1.315 and Gap: 0.005 EURAUD: Starting Price (Bottom):1.59 and Gap: 0.005 USDJPY: Starting Price (Bottom):107 and Gap: 0.5 USDCHF: Starting Price (Bottom):0.97 and Gap: 0.0025 BTCUSD: Starting Price (Bottom):3200 and Gap: 100 XAUUSD: Starting Price (Bottom): 1230 and Gap: 5
These settings are the ones I use, but you could find better settings for yourself. It works very well on JPY pairs.