Yep the trailing green line is the Chikou Span. It's the current SP projected back 26 periods. It's mainly used to confirm bullish or bearish trends.
All Ichimoku indicators will act as support or resistance. So when the Chikou Span hits the candle sticks, Kumo, Tenkan Sen or Kijun Sen it's a sign the current area where the SP is trading will encounter support, resistance or consolidation
Below is the monthly chart for GXY. If the SP drops further & the Chikou Span starts to interact with any of the indicators or candle sticks it points to an area of support or consolidation in the current position of the SP. But the main support & resistance indicators are the Tenkan Sen & Kijun Sen and the SP will bounce off them often.
I'm not a good teacher I hope it all makes sense.
GXY Price at posting:
$3.52 Sentiment: Buy Disclosure: Held