Hey Hodor, if I haven't said it already: welcome to the forum!
Props for your decision to stay off gear, but even a bigger pat on the back for taking your time to read up on your own. I've talked to a lot of teens in the last few months and I am seriously amazed by how easily they would turn to gear, and how much pressure is put on them to get this mindset.
As for answering your question, I guess it's changed since from bulking to cutting? At your age, a drastic calorie restriction is hardly a good idea. I say that because your body is still in development and craves good nutrition to transition into an adult. Nor is a big calorie cut needed. If you already partake in a sport your cut will be a breeze, if you are only doing weight lifting it might take some time. Either way, for you it will be possible to shed fat while building muscle. If you are 18 now and you've been working out for 3 years; you started at 15ish? What sort of exercise have you been doing? What does your current workout look like?
Also, all good and true info from the posts above.
For diet, now is the time to start teaching yourself to eat well, develop good habits and break bad habits. By "eat well" I don't mean to eat lavish or expensive, but rather learn to discern between unprocessed whole foods and palatable "food-like-substances". Yes that's an actual term. Here are some general guidelines to get started so long while you figure out how calories and macros work:
1. Think of your weekly diet and write down all the meals you usually eat in an average day. Some of them will be the same everyday, like oatmeal and eggs for breakie. That's no problem, in fact that's an easy "control group".
2. Cross out all the fast food, junk food, and unhealthy convenience food.
3. Cross out all the unhealthy drinks. Juices, sodas, milkshakes, Milo... You get the idea.
4. Make sure there is protein in every meal. Including snacks, in fact from now on snacks count as meals.
Okay might seem like basic shit, but I didn't really know if I should advise for cutting or bulking so I hope it helps.
Oh and as a bonus, here is a simple cheat sheet, because pictures are awesome.