The starter motor is at the back of the engine (usually on the driver's side) and works on the flywheel to crank the engine over when you turn the key. Have a look for it under where your brake booster is, it should look like this:
Using a hammer won't help unless you wanna bash at it in frustration - but hey, that might work too!
The source of the problem could be the solenoid on the starter motor, a loose wire from the starter to the body (earth) or the battery to the starter, a problem with the ignition barrel, loose wiring anywhere between the starter and the barrel, or something as simple as a blown fuse somewhere.
Start with the simple things (fuses), then work your way along from there.