\label{key}
A \label command appearing in ordinary text assigns to the key the
number of the current sectional unit; one appearing inside a numbered
environment assigns that number to the key.
A key can consist of any sequence of letters, digits, or punctuation characters. Upper- and lowercase letters are different.
\pageref{key}
The \pageref command produces the page number of the place in the text
where the corresponding \label command appears.
\ref{key}
The \ref command produces the number of the sectional unit, equation
number, ... of the corresponding \label command.