Support: In a downtrend, prices fall because there is an excess of supply over demand. The lower prices go, the more attractive, the underlying could get, for a gush of demand to come in from the buyers, there may be a point where an equilibrium point is reached where demand and supply match. This is support, it could be a price point or a zone.
Resistance: Resistance is the opposite of support. Prices move up because there is more demand than supply. As prices move higher, there will come a point when selling will increase, till the prices reach a point, where the selling (supply) matches the buying in the underlying. This point or zone is referred to as Resistance.
Once an area or “zone” of support or resistance has been identified, those price levels can serve as potential entry or exit points because, close to the zone of resistance/support, the underlying prices will do one of two things: bounce from the support or resistance level, changing price trajectory or violate the support during a bear trend and continue falling until it hits the next technical price zone (support). While a similar nuance can be observed in a bull market, where prices rise and when reach a resistance could reverse trajectory or break out and continue its bullish fervour.
Traders juxtapose technical levels, mentioned above, with several other technical indicators including RSI, Volumes, MACD, etc. to gauge and forecast if it’s a turning point or breakout/breakdown scenario.