One reason for numbering things like figures and equations is to refer the reader to them, as in "See Figure 3 for more details."
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.