Easy test for your starter:
First, note there should be just two wires that go to your starter: One giant one from the battery which obviously runs the starter motor, and the second one which engages the solenoid and trips a relay inside to engage the starter motor.
So, simply remove the small wire from the starter, and then using something like a screwdriver or a pair of pliers, touch the now exposed wire terminal to the giant wire from the battery.
Of course, be sure you are in nuetral and have the parking brake on first!!!
If your starter is working, it'll turn over just like when you turn the key. If it does not turn over, then your starter is probably defective. However, sometimes it's just the solenoid on the starter. To test that, let the car cool down and it if it starts. If not, get a hammer and shack the side of the solenoid once or twice. The idea is that the cylinder inside is jammed, and whacking it will knock it loose. Most starters have seperate solenoids, so if that is the problem, you can just unbolt it and put a new one on. Often older solenoids would heat up and the expand, and because of dirt inside, then would get jammed. Or, they just plain wear out.
Good luck!