Where do I start with updrades on my 2015 Honda Civic Si?

I don't know much about car but I'm trying to learn as I go. I don't know where to start or what to get to slowly start uprgading my car. I need some advice.

I'm not sure what updrades or uprgades are since neither are words. Assuming you meant upgrades, be very careful about upgrades to a brand new car - many things that people do will possibly risk voiding the warranty - it would be very foolish to buy a brand new car with a 5 year powertrain warranty and then do something right off the bat that voids it. Focus your upgrades on things not relating to the engine - new speakers or wheels or stuff like that. Don't even think about chips or turbos, and CAI's are a waste of money.

First go over to youtube and look up mighty car mods and subscribe to them, they have exactly what your looking for. First upgrade would be sound system then maybe air intake system. Those are usually the first two people jump on.

It is a brand new car, it doesn't need any "upgrades" except an air freshener.

If warranty stuff isn't an issue for you, then the very first mods where you will hear/see a nice change is in Header, Intake, and exhaust. I'm not familiar with the brand new Hondas, but I've had quite a few and once these mods are done… When you get on it, that Vtech cracks and you'll be pleasantly happy. Now don't be put off by 'exhaust' upgrades as there are some nice sounding exhausts that don't have your neighbors hearing you come for miles. Enjoy the car, and if you keep up on regular maintenance, you'll be able to keep that car forever. (Going on 320,000 miles on a 92 Prelude, original motor and 5 speed!)