The concepts of demand and supply zones are used to identify potential areas where price may reverse or pause. Here's a simple explanation 

DEMAND ZONE

A demand zone is a price area where buyers are likely to enter the market with strong interest. This usually causes the price to bounce, rejection by force of demand or rise from that level.

SUPPLY ZONE 

A supply zone is a price area where sellers are likely to enter the market aggressively. This usually causes the price to fall from that level.

USES IN FUTURE TRADING 

Traders use these zones to:

Identify entry and exit points

Place stop-losses and targets

Trade breakouts or reversals