Typically, they have two lugs (not counting ground) to which to connect wires.
2\ what is the meaning of hot wire / And way it calls hot ?
This is the one that has voltage relative to a ground reference. I assume it is called hot because you don't want to touch it. It is the one that is powered. It will hurt (burn?)
3\ explain the safety methods ?
Don't play with electricity. Turn off power before working on electrical systems and verify. Don't stick a knife in a receptacle. Don't open electrical devices when powered and, sometimes, even when not.
4\ what are the hazards of electricity ?
The risk of getting electrocuted. At that point, you won't care whether it was voltage or current.