Support and Resistance is one of the most used techniques in technical analysis based on a concept that's easy to understand but difficult to master. It identifies price levels where historically the price reacted either by reversing or at least by slowing down and prior price behavior at these levels can leave clues for future price behavior. There are many different ways to identify these levels and to apply them in trading. Support and Resistance levels can be identifiable turning points, areas of congestion or psychological levels (round numbers that traders attach significance to). The higher the timeframe, the more relevant the levels become.
Finding the most important ones can take many hours of practice. They exist due to an influx of buyers or sellers at key junctures. The fact that these levels flip roles between support and resistance can be used to determine the range of a market, trade reversals, bounces or breakouts. Each of these trades will have their own rules for entry and exit. TradingView has a smart drawing tool that allows users to visually identify these levels on a chart.