Const T & vs. T &&

I have the following function:

T foo();

And, in another function, I play with the returned value T, for example:

const T& t = foo();

or

T&& t = foo();

I want to ask:

• Are both equivalent?

• It is clear, what is the difference between these two approaches?

• I know that in the first approach, the temporal value of the lifetime corresponds to the reference lifetime. Does the same thing happen when using the rvalue reference?

• Should I even use const rvalue ( const T&&) reference ?

I use the first approach, this is what I'm used to, and it treats me well. I am still wrapping my head with rvalue and C ++ 11 links.