What's the difference between should/ought to/had better ? I should do my homework. I ought to do my homework. I had better do my homework. How i know when to use each one?

Why I am stuying a Master Degree? I'm 23 years old and i'm from México, i'm interested in technologies and investigation. This is the main reason why im stuying this. Beside, México is big country with a lot of resources, but there's not enough experts in many areas and for this reason my country is not exploting all the resources to be a world power. I'm trying to be an expert in technologies and help to teach another students.