The scalpers make a lot of "little" trade per day. They often work on a very short time frame (1 second to 1 minute).
To scalp the market should be volatil and liquid. The forex is perfect.

The scalpers win (or lose) few pips per trade but make hundreds of trades during a trading day.

A perfect (and fictive) scalping session on EURUSD. The pair move in a 20 pips range, the scalper buys the support and sells the resistance. It's a 1 minute chart:

Click to view attachment

It seems really profitable but it's hard to win in the long term