If you want to change how LaTeX treats a certain section of text
(for instance changing the type style), you have to specify what text.
In LaTeX lingo, you need to indicate the scope of the
command you are using to change the environment. For small
sections of text, this is done by starting the environment
with an open brace ({) character, followed by the command to
change the defaults, and ending with the close brace }
character. For example, to emphasize some text, like this,
you should type {\em like this}. This limits the scope
of the emphasize command to the environment within the braces.
An environment can also be delimited with a begin-end pair. This is quite useful for larger sections of text. For example, to center multiple lines of text,
like
these two,
you could use the following lines:
\begin{center}
like\\
these two,
\end{center}
Note the \\ following the first line. This is a
command which tells LaTeX to break the line at that point, rather
than filling the text completely between the two margins like it
normally does. This allows you to force lines to end when you want
them to, rather than when LaTeX wants them to.