In a long paper, you will often want to say things like ``See Subsection 2.5.'' This is called a cross-reference. If you actually type numbers like ``2.5'' into the paper, though, you run into a problem when you add or delete sections, since that will change the numbering. You would have to hunt down all the cross-references in your paper and change the numbers.
LATEX has a cross-referencing
system that makes this unnecessary. The idea is
to associate a label or name to each place that you
might want to reference. You do this with
the \label command, which can immediately
follow any command that uses automatic numbering,
such as \section. The parameter to
\label is a mnemonic name for the reference.
LATEX will associate the actual number with this
mnemonic name. For example, \section{Introduction}\label{S-intro}
associates the mnemonic name S-intro with the section
number for a section named ``Introduction.'' Later, you can retrieve the number
by using the \ref command. This command
takes the mnemonic name as a parameter. LATEX replaces
the \ref command with the actual number associated
with the mnemonic name. In our example,
\ref{S-intro} would be replaced in the output
with the section number of the ``Introduction'' section.
One fine point: When you use cross-references, you should process the LATEX input file twice. The first time allows LATEX to gather the reference numbers. The second time through, LATEX will insert the correct numbers in the correct places. (The numbers are actually stored in a separate file that LATEX creates automatically.)
LATEX is capable of helping with other bookkeeping chores as well. It can make a table of contents. It can number figures and tables and make cross-references to them. It provides a fairly easy way of creating an index for the document. And it has a bibliography environment that makes it easy to include citations to your references. If you are interested in any of this, it's time to start looking for a more comprehensive LATEX reference...