One reason for numbering things like figures and equations is to refer
the reader to them, as in "See Figure 3 for more details."
Sections, Equations, Tables, etc.
One can generate numbered references to anything for which LaTeX
maintains a counter by placing a
\label command
with some mnemonic name in the appropriate
environment. The reference is then generated
by use of the \ref command with the
same mnemonic.
For example
\begin{equation}
\label{eqno1}
c \geq\sqrt{a^2+b^2+1}
\end{equation}
.... intervening text ...
From Eq.~(\ref{eqno1}) we see ...
Assuming that this is the first equation,
the last line will produce "From Eq. (1) we see ..." Note the
use of the ~
to ensure that there is no line break between "Eq." and "(1)."
Also note that the \ref command produces only the number;
if you want the number to be in parentheses (as shown here) you have
to include them in your text.
Bibliographic citations
Bibliographic citations work somewhat differently. The following
should be consulted: