You should substitute each of the values in the domain for x in the f(x) equation and g(x) equation too. You do this until f(x)=g(x). Remember to only compare results from the same values in domain. Does this help? Let me know if you need any help. I could also help you solve it if you would post the equations for f(x) and g(x).
For -3, f(x)=3(-3)-4=-9-4=-13
g(x)=(-3)^2 -2=9-2=7 Not the answer since f(x) ≠g(x)
For -1, f(x)=3(-1)-4=-3-4=-7
g(x)=(-1)^2 -2=1-2=-1 Not the answer since f(x) ≠g(x)
For 0, f(x)= 3(0)-4=0-4=-4
g(x)=(0)^2 -2=0-2=-2 Not the answer since f(x) ≠g(x)
For 2, f(x)=3(2)-4=6-4=2
g(x)=(2)^2 -2= 4-2 =2 This is the answer since f(x)=g(x)
For 5, f(x)=3(5)-4=15-4=11
g(x)=(5)^2 -2=25-2=23 Not the answer since f(x) ≠g(x)