The great thing about romance and sexuality is that you get to explore it. It can often be an amazing journey of self-discovery. Labels are only as important as you make them out to be. You're fourteen. That's quite young, and it's understandable you aren't sure what you want. You've got a lot of time to grow and figure it out, so my hope is that you don't put too much pressure on yourself to do so.
I can't tell you exactly how you "know." I don't know if there is such a thing. I first thought I was bisexual when I was fifteen and I fell in love with my best friend. In my early twenties that turned into pansexual: I was romantically and sexually attracted to people regardless of gender (please note that you can have a different alignment between romance and sexuality; I just happened to be pan for both). Now that I'm almost thirty not only have I discovered more about gender (I'm non-binary), but I have almost zero attraction to males, so I identify as "homoflexible." For simplicity's sake I say I'm gay.
My point in telling you that is that it can be a long journey. Hell, I'm betting it's not over for me yet, and it's only just beginning for you! You'll find what makes you happiest in time. As for telling your parents, it's hard to say what's best. So many parents take a different approach to finding out their child isn't cis and/or straight. I think you know them best and only you can really decide whether you should tell them or not. Whatever you decide, it's okay. You are valid and worthy of love.
Good luck and
PM me if you need anything else. You've got this!