You just do it, basically.
It's legitimately scary but you get used to it and it gets less scary. You just put one foot in front of the other, focus on what is right in front of you, and you lean on whoever is in your life and will support you.
I remember feeling so extremely vulnerable and scared when I first socially transitioned and sitting down to google "how to deal with feeling so vulnerable". It really is overwhelming, I remember that. The first time I left my house in a dress, I thought I was going to be killed in the street. Just going out dressed as a woman and not being harassed or even noticed was really helpful for helping reduce my fears, it was exposure therapy - the more I did it, the less afraid I felt for next time.
This is a side note, but you are very young, and getting on HRT sooner vs later is an issue of harm reduction - I would highly recommend prioritizing that. I picked my chosen name when I was still a teenager, but didn't medically transition for decades after that - the regret is enormous, and this is a common and tragic story with trans people, so I always urge anyone to start HRT ASAP.
In the right doses and route of administration, HRT can help immensely, esp. with depression.
It does get better π«