The leading coefficient is the number in front of the variable with the largest exponent. The constant term is the number which does not have a variable attached to it, so it does not change, hence its constant nature.
Equation 1: Correct
0 = 3x^2 + 2x - 2
Equation 2: Incorrect
0 = -3x^2 + 1
Equation 3: Correct
0 = 3x^2 - 3x - 2
Equation 4: Incorrect
0 = 3x^2 + x + 2
Equation 5: Correct
0 = 3x^2 - 1x - 2
Hope this helps!! :)