{$foo}        <-- displaying a simple variable (non array/object)
{$foo[4]}     <-- display the 5th element of a zero-indexed array
{$foo.bar}    <-- display the "bar" key value of an array, similar to PHP $foo['bar']
{$foo.$bar}   <-- display variable key value of an array, similar to PHP $foo[$bar]
{$foo->bar}   <-- display the object property "bar"
{$foo->bar()} <-- display the return value of object method "bar"
{#foo#}       <-- display the config file variable "foo"
{$smarty.config.foo} <-- synonym for {#foo#}
{$foo[bar]}   <-- syntax only valid in a section loop, see {section}
{assign var=foo value="baa"}{$foo} <--  displays "baa", see {assign}

Many other combinations are allowed

{$foo.bar.baz}
{$foo.$bar.$baz}
{$foo[4].baz}
{$foo[4].$baz}
{$foo.bar.baz[4]}
{$foo->bar($baz,2,$bar)} <-- passing parameters
{"foo"}       <-- static values are allowed