\begin{array}{col1col2...coln}
column 1 entry & column 2 entry ... & column n entry \\
.
.
.
\end{array}
Math arrays are produced with the array environment. It has a single
mandatory argument describing the number of columns and the alignment
within them. Each column, coln, is specified by a single letter
that tells how items in that row should be formatted.
c -- for centred
l -- for flush left
r -- for flush right
Column entries must be separated by an &. Column entries may
include other LaTeX commands. Each row of the array must be terminated
with the string \\.
Note that the array environment can only be used in math mode, so
normally it is used inside an equation environment.