How it is finding the engine problems in vehicles by using the help of computer technology?

I LOVE TO ANSWER THIS ONE CAUSE I DO IT DAILY

FIRST YOU HAVE TO GET GOOD SCANER BY THE WAY I HAVE THREE KINDS LUNCH, MENTO TOUCH AND MACTOOLS

WHEN YOU CONECT THE COMPUTER YOU HAVE TO FIND OUT THE TROUBLE CODE AND WORK IN IT BUT YOU HAVE TO KNOW SOME OF THE CODES IS SHOWN UP AND EASY BUT ALOT OF THEM IS NOT EASY AND RELATED TO OTHER THINGS YOU HAVE TO FIND OUT AND TRY TO GET THE RIGHT SOLUTION AS EXAMPE THE TROUBLE CODE   ( P0300

IT SAYS MULTIPLY MISFIRING YOU HAVE TO TEST LIKE10 ITEMS STARE BY SPARK PLUGS AND IGNITION COILS TO THE END OF CATALYTIC AND EVAP SYSTEM AND SO OM