You care about this girl, but you don't know how to show her. Be sure to listen to her when she needs a kind ear; be courteous and chivalrous whenever possible; and don't be afraid to tell her how you feel. Make her feel appreciated through your words and deeds.
Method One of Three:
Listening to Her
1
Get to know her. If you're in school together, talk to her in class. If you have mutual friends, talk to her whenever that group gets together. You don't have to make a big deal about it – just say hello and smile at her. Ask her how she's doing, and strike up a conversation. The first step to showing her you care is getting to know her.
If you make the effort to talk to her, she will get the idea that you care about her – especially if you make a habit of asking her how she's doing. This is a low-risk way to show her that you're interested.
The better you get to know her, the easier it will be to show her that you care. Also, getting to know her may make you care about her more – and her care for you may also blossom!
2
Text with her and talk to her online. If you can't spend much time with her in person, this is a great way to get to know her. Even if you see her 
every day, however, social media and other instant messaging apps can be great be a great way to talk to her one-on-one.
3
Be genuinely interested in what she has to say. Ask her questions, and listen carefully to the answers. Respond thoughtfully with more questions, and try to learn about her. Take active interest in her activities, without being too nosy or overbearing. Listening is one of the best ways to show that you care.
Start with basic questions: "How's your day going?" or "How was your weekend?" or "Nice shirt – that's my favorite band! Do you like them?"
Segue into more advanced questions: "How did that [specific thing] go?" or "Do you go there a lot?" or "Have you ever seen them live?"
Don't only ask questions, or you might make her uncomfortable. Share your own experiences, and make jokes. Have a conversation, not an interrogation.
4
Listen when she needs to talk. Be a kind and patient ear. Encourage her when she feels uncertain, but try not to throw too much of your own opinion into the mix. Offering thoughtful advice can be a great way to show care, but sometimes people just need to talk through their problems. Do not listen with the aim of getting anything from her; listen purely because you care.
5
Remember things that she says. Remember the details and the specifics, and bring them up when you get the chance so she knows you heard her. This is especially true if she's said something important! Retaining information is an important part of listening.
She may find it irritating if you zone out and forget things that she has told you – whether these are things that she wants you to do, or just details from her life.
Remember the little things she says; things that are just comments or sayings. For instance: if she just at some point mentioned that she has always wanted to go to the lighthouse, plan a surprise trip and take her there. She will appreciate that you remembered a small comment and made it come true.
6
Respect her values and beliefs. She may do things that you don't approve of. Don't restrict her, unless these things harm her in a big way. If a value is special to her and is a part of her life, you should respect it even if you don't like it – and she will appreciate you for that. Respect doesn't mean that you must be a subordinate; it just means that you should let her be an individual.