Support and resistance are highlighted with horizontal or angled lines, called trendlines. If the price stalls and reverses in the same price area on two different occasions in succession, then a horizontal line is drawn to show that the market is struggling to move past that area.
In an uptrend, the price makes higher highs and higher lows. In a downtrend, the price makes lower lows and lower highs. Connect the highs and lows during a trend. Then extend that line out to the right to see where the price may potentiall