First of all, I am super new and this is my first ever Arduino project. I have a basic knowledge of Electrical Engineering but I do have some experience with writing code.
Basically, I want to press a button to load an audio file stored in an SD card and play it through an external speaker connected via a 3.5mm audio jack - like how I would play audio from a PC.
Not possible from an Arduino.
You will need a sound shield, or music shield- it's been a while since I've used one. My last project with sound ran on a Wemos D1 Mini with a DFPlayer Mini Module.