Hey there, friend –
Great news: you’re off to a great start!
Being non-binary just means that you don’t quite feel like being a girl or a boy is the right fit for you. That even though everyone has always told you you’re a girl, and you’re biologically a girl, it’s not a perfect word for your gender, and that you don’t feel like you’re a boy either. So if you’re wondering if you might be non-binary, then congratulations! You can be non-binary!
A place that might have some good terms to help you out if you’re still not sure is the Non-Binary Wiki. It has many different words to describe gender that doesn’t fall strictly into ‘boy’ or ‘girl’.
There are many, many words for gender that people have come up with and use to describe themselves. You get to look at your gender and go “hm, this one isn’t quite right – what if I try another one?” You can try on different gender words and different pronouns for as long as you want, as many times as you want, until you find the one that feels like a good fit for you.
The next step is just going out and doing it! Ask people to call you by the name you’ve picked out. Let people know that your pronouns are now they/them. If you want to bind, that is also great, but keep in mind that unsafe binding practices can be really dangerous for your health. Please check out this Binding 101 article with safety information.
Good luck trying on your new identity, and feel free to write me back if you have any other questions!