If you only put a little bit of bad gas in your cars gas tank it may not cause a problem or may cause a simple problem that goes away after awhile.
But the most common symptoms that you have bad gas in your cars gas tank are rough engine idling, engine stalling, hard starting or no start at all.
If you got bad gas at a gas station you need to take the car to a mechanic and have them drain the gas tank and remove the bad gas.
Then put fresh gas in along with a new fuel filter.
If the gas station is at fault for the bad gas you should report it to them and they should pay for the repairs to your vehicle.
It's always best to wait to get gas after they fill the fuel tanks and not during because when fuel tanks are being filled at gas stations stuff at the bottom can get stirred up and then get pumped out and into your gas tank.
There also have been some issues with diesel being accidentally put into the gas storage tank at the gas station.
They really should have different size hoses for the tanker truck to fill the fuel storage tanks so that a fuel delivery is not done incorrectly.