Spanish Grammar question?

What is the difference between when someone says "me canto" compared to "yo canto" or just "canto" this isnt the only times ive heard it. For example "espero que te sientas mas bien" wouldnt it read i hope that you feel yourself better? I dont get why we couldnt say "espero que sientas mas bien" not trying to make fun of the language, because I really want to learn it, but would like to understand it better.