I was told I sing through my nose? How do I fix that? And how can I stop my voice from crackling on the scale?

For the nasally singing, I suggest making sure you're singing with you're diaphragm (breath with your stomach and make sure your shoulders aren't moving when you do so), also try opening up the back of your throat (I'm not sure how to explain that one, you just have to experiment) and use a lot of air, and get a private teacher if you care that much about it, one could really help.