The average price, with recent candles counting more.
An EMA smooths the price into one line. Unlike a simple average it gives the newest candles the most weight, so it turns sooner when the market turns.
Short EMAs (9, 21) follow the price closely; long ones (50, 200) show the bigger trend. Price above a rising EMA is the classic definition of an uptrend.
Worked out by the same code the builder uses, on stored daily candles. Move a setting and the line moves with it. This is what happened, not what will happen.
Gate: EMA(200) [1d] is rising, so you only trade when the daily trend points up.
A cross of two EMAs is late by design: by the time the lines cross, much of the move has happened. Crosses work better as a filter than as a buy signal.
No indicator predicts the market on its own. Build the rule, then test it on years of history with fees included. Try TradeXtool free for 14 days.