So trans or being a girl is pretty vague. I find it helpful to think of the specific aspects or changes that would make you happy.
Like, name, pronouns, clothing, changes from hormones, how people treat you etc. This site can be helpful:
https://genderkit.org.uk/
+1 to what mizu said about shared experiences. Here is a site that talks about it pretty well:
https://genderdysphoria.fyi/
Aand I'd also say, don't be afraid to experiment with things (be safe while you do though!), somewhere down the line if you end up findings out you aren't trans or indeed a girl, that's also okay.