Prices trend. Trendlines are drawn by connecting two or more points of support and resistance. An uptrend means a series of price bars or candles exhibiting higher lows, higher highs or higher closes. Similarly, a downtrend means a series of price bars or candles showing lower highs, lowers lows or lower closes.
An uptrend line or support is drawn by connecting the higher lows with a straight line and extending that into the future. Similarly, a downtrend line or resistance is drawn by connecting the lower highs with a straight line and extending that into the future.