Look up an eBook called The Sexual Key, it's a pretty much amazing book that goes over the emotional state of women and how and why they react to things so differently from men, one of the best reads I've ever had.
Anyways, my take on the questions, and I'm assuming you're a high-schooler, like myself, so we'll go with a typical high-school setting/situation, just being in class together:
1) When she keeps glancing over at you, it's a sign that she's interested(unless you're doing something really weird), but make sure you don't start doing the same, women prefer guys who seem to have their own thing going, and aren't easily deterred by some girl glancing at them. Honestly, I would try to figure out what her intelligence level is a bit before trying anything, because different levels of girls respond better to different actions, your personality in the class also needs to be taken into account.
For example, I tend to be one of the most outspoken people in the class, as least during teacher's lessons, I'm extremely satirical/sarcastic and tend to be in a good mood. If the girl seems pretty chill but socially able, I might catch her in one of her glances one time, look her right in the eye, and give her a sideways smile and a wink. For me it works like a charm, it acts as basically a silent icebreaker, and when I chat with her a few minutes later we're both significantly more open. Once again, you really have to change it up depending on your personality, I'm a bit of a jokester, so by being very blunt and forward, and basically saying everything I'm thinking out loud, I come off really well, but it doesn't work for everyone, figure out something that suits you.
For #2, it's like I was saying, women are interested in men who seem to have their own life and their own plans going, not the guy who gets distracted from his plans by a few glances. Women want the typical romance-novel hero. He's disinterested in the woman, his life, his goals, and his quest take precedence over her, but that only makes her even more crazy about him. Don't try to confront her, or get her to notice you, have fun, be yourself, hang out with your bros(chicks dig guys with lots of bros), don't swoon over her, she wants you to be independent. After a bit of that, she'll turn into #1 situation, and you can go from there.
None.