I didn’t know I had to file taxes on the stocks I sold, so I didn’t.

Ive gotten stocks and purchased stocks through my employer through Fidelity for the past three years. I trade them once they vest and I’ve earned about $3000 It never occurred to me that I would need to file taxes on them because they already withhold stocks once they’re distributed.
How much trouble am I in? How do I file taxes for previous years? When I go to Fidelity and look around, I see consolidated form 1099s, but there’s nothing to fill out on there.