My perspective is from having MtF hormones and vaginoplasty. There are many other treatments, and people who have had those will likely have very different (yet really neat) answers.
I've been coming up against this question a lot lately. I'm not claiming to be an expert now, but I've learned a lot more, and have developed thoughts and theories to explain some of the issues we face now.
I will fight for my rights until my dying breath (which, let's be honest, feels a lot closer now than it did before); I wish I didn't have to. But I need help. I am under attack, and I'm sounding the alarm.
In this post, I ask myself questions that get more into my personal relationship with God, especially as it relates to gender.
A person successfully and convincingly presenting themselves as a cisgender member of a gender they were not assigned at birth is called "passing". Passing is a complicated and controversial topic, partly because of the issues that it raises for both those who can and cannot pass. It's also a philosophical issue, a safety issue, and a social issue (and a variety of other categories).
I've recently come to realize that I'm genderfluid. No, I'm not some puddle, and you can't use a mop to clean me up (well I suppose you could, but I wouldn't let you). I'm genderfluid: I experience my sense of my own gender as an frequently-changing place somewhere on the gender spectrum; and sometimes multiple places on the spectrum simultaneously; and sometimes I'm not even on the spectrum. Confused? Me, too!