Delimiters (parentheses, braces, brackets. ...)
Command	Example	Result
\left(... \right)	$$2\left(a+b\right)$$	$2~\left(a+b\right)$
\left[... \right]	$$\left[a^2+b^2~\right]$$	$\left[a^2+b^2~\right]$
\left{... \right}	$$\left{x^2, x^3, x^4,... \right}$$	$\left{x^2, x^3, x^4,... \right}$
\left\langle... \right\rangle	$$\left\langle a,b~\right\rangle$$	$\left\langle a,b~\right\rangle$
\left\| ... \right\|	$$\det\left\|\array{a&b\\c&d}\right\| $$	$\det\left\|\array{a&b\\c&d}\right\|$
\left\\| ... \right\\|	$$\left\\|f~\right\\|$$	$\left\\|f~\right\\|$
\left{ ... \right. (note the dot!)	$$f(x)=\left{{x^2, \rm~if x>-1\atop~0, \rm~else}\right.$$ (\rm switches to roman style)	$f(x)=\left{{x^2, \rm~if x>-1\atop~0, \rm~else}\right.$
\left.{ ... \right\} (note the dot!)	$$\left.{{\rm~term1\atop\rm~term2}\right}=y$$	$\left.{{\rm~term1\atop \rm~term2}\right}=y$

Note: The delimiters are automatically sizes.