if f(x)=1-3x and g(x)=x^2-1, find :

g(g(x)), and
g(f(x))

what's the trouble? Just substitute and evaluate:

g(x) = x^2-1, so
g(g) = g^2-1 = (x^2-1)^2-1
g(f) = f^2-1 = (1-3x)^2-1