How to fix Engine that won't restart?

How to fix Engine that won't restart?
Life experience has given me this info. It could be a hand full of things, but without seeing/hearing our car I can only venture guesses.

If you turn the key and...

you hear a click but theres no movement after, its more than likely the starter motor, it could also be the relay that connects your starter to the ignition. The click is the power clicking on in the relay, its possible its just not sending it after that, but my guess would still be the starter motor, if you have it out of the car autozone will test it.

you hear the starter spinning but not the engine its the starter, it has to clutch in and out so that its not running while the cars running, failure to crank the engine while spinning is a result of this just breaking down, you'll need a new starter motor.

you hear the engine cranking but you're not getting and kind of combustion, this could be a few things, if it smells like fumes it could be that your spark plugs, wires, or distributor(or coil pack) have gone bad, if its none of those it could be that a fuel line/filter/injector is clogged. If you can clear the clog, great, otherwise, replace the parts.

you hear nothing, this is the ignition switch, which is where you're turning your key. Something isn't right in there and its not completeling the circuit like you want it to, to test this theory you'll need a friend, get a voltage tester, they have tons of these for cars and they all come with instructions and can be as cheap as 20 bucks, basically what you want to see is if you're getting any voltage, so while one person turns the key the other is touching the different parts of the starter relay. The thin red wire is typically the one that comes from the ignition switch.

If none of those are the case, you're over my head. Wear eye protection when you're under the hood, that thing is no joke, a car battery is 12 volts, while its the amps that kill you, 12 volts can still ruin your day.