Ah, crushes. We all have them, and it can be really hard to talk to them when we want to. Our throat can become dry, our legs can become weak and our body can just feel unsteady. The best way to talk to them is to imagine that you are talking to a friend. It helps because we feel more comfortable and less anxious. It's mainly being anxious anyway.
Because you are focussing on succeed. When you are focussing on the result of an action you can't "enjoy" doing it, the action is just something you do to get something and not an extraordinary an unique experience in your life.
Everyone has a crush and that is something nobody should be ashamed of having, when it comes to making the first move you might feel nervous or scared, but thats okay. You're the only one who places a real limit when it comes to making the first move, so technically the reason you can't talk with your crush its because you're nervous and maybe you block yourself around him/her. Remember you're both human and its okay to be scared, think of him/her as just another friend when you're around your crush. I wish you all the luck in the world!
This sounds like a pretty normal thing. Are you controlling your breathing? Have you though ahead what you would like to say? Is your heart racing? If so, you can practice some calming activities and breathing exercises. Practice what you would say with a friend, like role play. Once you build up your confidence, you will be able to do it.
It's likely connected to some sort of personal insecurity, like to fear of being judged or rejected. Sometimes it helps to take things step by step, slowly, without pushing yourself too much. That could mean starting with talking about simple things, in contexts you are more comfortable in, for example when there are other people around. You'll see where to go from there. You don't need to have it all planned right now, you'll see how things develop and maybe you'll feel more comfortable as you start getting closer to her.
Sometimes when we have a crush on someone we idolize them a bit, and that makes talking to them very daunting. It can also feel like anything we could say to them would come off as silly, and having a crush can also make us nervous, which makes it more likely to stumble over words or not know what to say.