When your Car starts but stalls after a few seconds?

Depends on if your vehicle is carbureted or has EFI. If it's a carbureted engine, then the carburetor's choke valve may need tuning. If it's EFI, then the voltage regulator could have shorted and that would cause a certain spark plug to short out so when that spark plug would attempt to fire, the ignition order would blow out of sequence and cause a stall in the car. If your car is EFI, then remove your suppression cables and check the spark plugs. If you have a bad spark plug, replace the spark plug and if the problem persists or if the same spark plug goes bad shortly after, then have a mechanic look at your voltage regulator, ignition coil, starter solenoid, starter relay, and ignition module.