I stumbled upon this question in my text book :

Let f and g be polynomials defined by f(x)=x-1 and g(x)=x^2 -1.

Find formulas for f o g and g o f.

I dont fully understand what they mean by finding a formula.

so we no fog = (x^2-1)-1 = x^2-2

and gof =(x-1)^2 -1= x^2-2x

Soo how exactaly do we find a formula?