Support and Resistance levels are comes under price action trading. Most of the intraday and swing traders are pure price action based traders.

Support is the level where there are buyers and the Resistance is the level where there are more sellers.

Most of the buyers are activated at the support level since they thing that is the best price to buy. So the price of the stock increases when the buying activity begins.

Similarly most of the sellers get activated at the resistance levels since they think that is the best price to sell. The price of the stock gradually goes down when the sellers get activated.

But not all the times the price reverses at the support and resistance levels. The probability is high.