You may want to review operations on functions first.
Another thing you can do to two functions is to compose them. That means you apply one and then the other. For example, if f(x) = −2x + 1 and g(x) = x2 − 1, you could be asked for f(g(−1)). First, you find g(−1), which is 0. Then, you find f(0), which is 1, so that's the answer.
Remember to always apply the inner function first!