Error codes: P0300,P0304
Knowledge level: I know little about cars
Help needed: Please help me find out what is going on and how to fix it.
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Those are misfire codes. You've likely got a problem with either the ignition or fuel delivery systems (or both).
I would venture to propose that if you "know little about cars" then you are not equipped to diagnose issues with the coils, spark plugs, ignition wires, injectors, etc.
Although I would not usually propose throwing parts at a problem without some investigation as to the root cause, the age of your car means it is likely due for new spark plugs and ignition wires anyway.
I would start with buying a repair manual, then proceed with replacing the plugs and wires as these are common causes of misfires. Injectors and coil pack would be next on my checklist.
As stated in the other answer, the most likely cause is spark plugs ($15-$20 for a full set) or coils (about $20 each). A repair manual (Haynes or Chilton) that is specific to your vehicle will cost about $20-$30 and will tell you not only how to do this, but many other repair tasks that you are getting raped for at a mechanic shop, like changing the bulbs for brake lights and turn signals.
The tools needed for this are very rudimentary, and you may have them already. A ratchet with a set of sockets, or a set of wrenches, ideally both. For spark plugs, you will need a spark plug socket, ratchet and ratchet extension. Many "ratchet and socket" toolkits have a spark plug socket included. If you need tools, pawnshops are a great place to get wrenches and sockets.
I've worked on a Hyundai Accent before for this specific problem (I think it was a 2008), you will need to: