What is the difference between these two words?

As far as I can tell they both mean "it is possible".

And another thing, why is it better to ask, "У тебя всё хорошо?", rather than "Тебе всё хорошо?"?

I read that "category of state" words eg. (холодно, нужно и хорошо) always go with a pronoun in the Dative case. For example, "Мне холодно".

Yours confused as ever,

D.

Any help will be appreciated.