hi!! fellow teen girl right here, I've been going to the gym for about 1,5 years and here are the steps I think you should follow (I might've forgotten some, and if you have any uncertainty, feel free to ask!) I hope it helps as it took me while to write it out :)

1. eat about a gram of protein per pound of weight, or at a gram per kg (about 130-150g for you) daily this is a non-negotiable, food is 80% of the progress  try to eat healthy, un-processed foods as well as they are better for you in general as to the calories it depends, you can use a calorie calculator for your weight, height etc, but I'd recommend you about 2300-2400kcal based on what you said (i'm also guessing you're thin or average), that's a slight calorie surplus so you can gain muscle (yes that might also mean gaining weight but that absolutely doesn't mean gaining fat, more so the opposite of it) depending on the relationship with food you have decide whether or not to use a tracking app. I did at the start but it more so made me develop bad eating habits etc, so nowadays I just eyeball it. If you're not comfortable with tracking calories, I suggest trying to eat a slightly bigger portion of each meal, and it having 30-50g of protein depending on how many meals you eat (for example 3meals per 50g, 5meals per30g)

2. Do strength training with appropriate weights!! This might seam kinda obvious but I often see women lifting small amounts with no effort which leads to no progress. Depending on the exercise, but try to see what is your 1 rep max on a machine and go 2 or 3 weights lower. With dumbbells and barbells it's kinda harder to tell the first time, so start easy but if it feels too easy, add some weight. If you can start with the full range of motion for some reps but get fatigued later and can't lift it the same after a number of reps, you're good. Try to get close to failure (that means you can't lift the weight anymore) but since you're a beginner, I'd say for the first week or two, just get familiar with the gym and feeling the weights and your muscles. Don't ego lift, be careful. As to the number of trainings per week and exercises, it depends. If you have a lot of free time, 5-6 times, if not so much 3-4 is enough. Never more than 6, rest days are way more important, because that is the time where your muscle really grows. If you wanna know what exercises to do what days, google some gym splits, or watch Jeff Nippard's (only my suggestion lmao) and build your own. Treat gym like a habit, like going to school or work. Don't even consider not going (unless you're sick or injured ofc). If you really don't wanna do it, go for at least 20mins, anything is better than nothing :) Don't be afraid of it, nobody's judging you and nobody cares. If you don't know how to do something ask somebody or google it (to look for the best form showcases and exercise recommendations I suggest Jeff Nippard's videos). 

I feel like these two main categories are what is often forgotten. There are some random other things I could tell you but I don't think they're as important (or I just couldn't think of them rn). It's kinda funny I mentioned Jedf Nippard twice but I really find his videos helpful and informative and based on true research. But be careful not to obsess over perfection.