All commands which have more than one argument can be used in the following three ways:
\begin{bf}
Some text.
\end{bf}
\bf{Some text.}
{\bf Some text.}
With the third method, it is important that the command has its own pair of braces, and that the command immediately follows the first brace. Otherwise, the parser cannot parse the argument(s) properly. With multiple arguments, each should be enclosed in braces.
Optional arguments are specified using square brackets or parentheses.
Whitespace should be avoided between command names and their arguments.