Hi,
Indicators are used in strategies, when it's necessary to make some decision, for example, to close order, based on indicators calculated value. Here is a reference to the sample indicators usage
https://www.dukascopy.com/swiss/english/forex/jforex/forum/viewtopic.php?f=6&t=1038&hilit=context.getIndicators+ Yes, indicators calculate some values based on given instrument bid/ask price. Only candle data could be used to calculate indicator values.