Yes bad spark plugs can cause a car to not start or be hard to start.
A vehicles engine needs a few things to start and run and those things are spark, air and fuel.
If your vehicle is getting fuel and enough fuel pressure and your vehicle is still not starting then it could be the vehicle is not getting spark.
Some other things that could cause a no spark condition are bad ignition coils, bad spark plug wires, bad ignition module, bad distributor cap and rotor.
Some older vehicles had or have distributor caps and rotors and when those are bad the engine may not get spark.
A timing belt or timing chain could have gone bad causing the engine to jump out of time and when the engine is not timed properly it won't run correctly or at all.
If your timing belt has not been replaced and it's been 100,000 miles or more then it's usually time to change the timing belt.
If you haven't changed your spark plugs in 100,000 miles or more then it's time to change them anyway because it will help improve your fuel mileage and engine performance.
You can remove a spark plug and plug it into the the spark plug wire and touch it to the metal on the vehicle and crank the engine.
If you see spark then that's a good thing even though it could be a weak spark and the spark plugs still may need changed.
If your car still isn't starting after changing spark plugs, make sure your vehicle is getting enough fuel pressure and make sure the ignition coils are in good condition.
If your car has an ignition module and it fails then your car will stall and not start at all.
I would take the car to a mechanic who can plug in a diagnostic tool and tell exactly what could be causing your engine to not start.