The domain is the set of inputs is mapped to (like the real numbers, whole numbers etc) while the range is the set of inputs that the function maps to (i.e. the output).
Usually the range refers to the set which is the type of number (like the real numbers), but it doesn't necessarily have to only include possible outputs.
The co-domain is the actual set of possible outputs and it can be different from the range.
It might do you a service if you look at the Wikipedia entries.