This section describes the commands and features that take advantage of the parenthesis structure in a program, or help you keep it balanced.
When talking about these facilities, the term “parenthesis” also includes braces, brackets, or whatever delimiters are defined to match in pairs. The major mode controls which delimiters are significant, through the syntax table (see Syntax Tables in The Emacs Lisp Reference Manual). In Lisp, only parentheses count; in C, these commands apply to braces and brackets too.
You can use M-x check-parens to find any unbalanced parentheses and unbalanced string quotes in the buffer.