You may want to review positive exponents first.
Multiplying by something raised to a negative power is the same as dividing by the same thing raised to the positive power. For example, multiplying by a−2 and dividing by a2 are the same thing. So, if you have to simplify (−2 ⁄ a2)(−1)0(b2 ⁄ a)−2, you can rewrite it as (−2a−2)(−1)0(b2a−1)−2. (Remember that a is the same as a1, so dividing by a is the same as multiplying by a−1.) By what you already know, this is the same as −2b−4. But you want to write your final answer without negative exponents, so you rewrite it as −2 ⁄ b4.