The main way to tell if she like likes you is if she tucks her hair (if she has any) behind her ear when talking to you. This is like the most common sign that a girl is talking about something that she has romantic desires with. It's like the most basic body language for "dude i want your richard". to be certain, look out for this kind of body language. You don't want to interpret her wanting to hang out with you or talk to you as love, as it's literally what friends do on a daily basis.
If she likes you, then you really can't go wrong. You could be the typical social forgetup, possibly the worst, and she won't care. As long as you don't act super weird, she'll be interested in whatever you do, just act natural. If you ever find yourself at a loss of words or are feeling a little awkward, don't worry. She won't ever judge you for that.
If you're like, 100% certain that she likes you and you like her back, casually ask her on a date. Don't make it flashy or anything, just be like "hey want to go on a date?" or "want to get cheeseburgers or stuff?" It really doesn't matter the way you word it, just the notion of going with her to get food is already a win win since it gives you two some quality time. It'll also give you guys some time to learn more about each other.
According to your profile, you're 11.... Are you sure you need a relationship? What's wrong with just being normal friends?
Dude i'm 0 years old and i eat 3 square meals of clit every day
As far as dating advice goes, don't listen to dating advice unless it's from a certified source, aka not BLF