Why led is on when there is no input at terminal 1 &2 for 7432 IC?
1st question:

First of all, all unconnected pins are like little antennas, and maybe can have a floating voltage on it, possible from every radiation caught around it from wifi, tv, radio and so on. So to assure the LED will go off you have to short pins 1 and 2 to the GROUND. Only connecting they to zero voltage will guarantee the led to turn off.

2nd question: The OR gate actually look like this. You can see this circuit has 4 terminals besides the output: two digital inputs A and B (1 and 2 inputs at 7432) and two feeding pins (Vcc and Gnd). The OR gate does not copy the input as you were taught. Actualy it sends the same voltage expected by the OR table but from the Vcc(from the pin 14)