1.click the metal disc inside ,hand warmer will become hot instantly 

2.when the hand warmer become hot ,the liquid inside will become crystal gradully 

3.When hand warmer become not so cold ,you can put the hand warmer into boiling water for 5 to 10 minutes ,the crystal will become liquid as original one 

4.When hand warmer become cold ,you can click metal disc again to reuse it .