[boxhead]

Get someone who can help you, then look at the starter motor, you will see a small blade terminal, take this terminal off the starter solenoid and put the test light pointy end in the wire terminal. Connect the aligator terminal end of test light to a good earth.
Now get helper to turn ignition on, make sure immobiliser is off and get them to crank, the test light should light up, if it does then fault is in starter solenoid, if it does not then fault is in wiring from ignition switch to starter.
If you want to test the starter, then run a jump wire from a 12v supply to small terminal on starter, easiest way will be to get a 6 inch length of wire, crimp on a female blade terminal and bare the wires at other end.
Now connect the female terminal to small terminal on starter solenoid and contact large bolt power wire at starter motor solenoid (battery voltage) starter should crank over, if not then starter is no good.

If you have to gain access from under the car then make sure you have good jack stands and also make sure car is in neutral.

Another thought, is your car auto or manual, because if auto it could be in the neutral start switch. (if no test light in first test)