Your calculator will tell you -2.
Actually this is the answer to: "To which power do we have to raise 10 to get 0.01?".
10⁻² = 0.01
Then you can easily agree that log(1000) will be 3.
Now hopefully you understand logs.
Note, this is assuming we're dealing with log₁₀. You can also have logs with another base. The principle is the same.
