EA - the idea of such program is to trade, to create/modify/delete trades and orders and basically to control their count
Script - similar, but its code runs once
Indicator - the idea is to get information from the candles and transform that information to another kind of information
EAs and Indicators are little bit different. Yes, EAs can do calculations, because they are programs, but its better to make those calculations in indicators. Swing, highs, lows... there are some things already available in "Condition" block, such as the highest/lowest level in few candles, or pivot points, but for more complex problems indicators should be used.
I don't understand Andrew's Pitchfork. I only know that it has many coordinates. I have no idea how this thing is used.