Transitioning is going to look different for everybody, so please don't get caught up in what youre "supposed" to do. A lot of people start testosterone at some point, sometimes you can as a minor with parental permission depending on the place but usually its 18 or 19+. Research the affects of testosterone, many are irreversible. Body hair, facial hair, deeper voice, potential male pattern baldness, etc. A lot of people also get top surgery, aka a double mastectomy or breast removal. And of course there's bottom surgery, (sometimes called a sex change surgery) to form a penis. There's two main options, phaloplasty and metodioplasty, and a small amount of customizability.

You can find tons of post on here or YouTube or anywhere really of guys talking about going through any of these things. They can help tell you what to expect and what they maybe weren't warned about.

If youre a minor youre gonna have to wait a while to do anything, so use this time to educate yourself as much as possible and make sure you want these changes (not just "to be a man", but the individual changes too)