I have a 1998 Pontiac Sunfire and my question is what kind of modifications can I put on it

Modifications on a car like that are some what limited, if the car has high mileage a turbo is NOT recommended. Simple bolt ons such as a cold air kit, header and exhaust would be easier and cheaper. since this your first car, start small, don't go nuts, take your time and do your home work and later on when you get a better car you'll be better off.

Definitely what other guy said. Cold air intake(watch out for puddles) and a header,exhaust,muffler upgrade would give vast improvement in sound amd power. They sell chips and stuff but the factory intake is really restrictive. Just look at all those stock motor drag cars. I have an AEM intake and a 4 to1 header with stock exhaust piping and mine sounds very mild and I am upgrading soon. Also keep your overall weight down by keeping your tools, extra cases of water, and other junk out of the car and it will feel lighter and in turn faster. Also you can look into rebuilding the motor and having it bored out slightly. But don't forget to upgrade the suspension and brakes. Its one whole system. They all work together. Its why any high end car maker doesn't just jam the biggest motor possible in the tiniest car. Think Smart car with a 454 big block and manual drum brakes. Not a smart idea.