The product changes and cannot be reversed.
For example:
Wood burning in the fireplace. Ashes remain. You cannot revert the process and bring back the log of wood.
This is an example of chemical change
Physical change is when the product can be reversed.
For example:
If you mix salt in a glass of water. You mix it until it dissolves. You can bring back the salt by heating up the water in a pan. The water evaporates but the salt remains on the bottom.
This is an example of physical change.