LaTeX mode provides a few extra features not applicable to plain TeX:

C-c C-o

Insert \begin and \end for LaTeX block and position point on a line between them (latex-insert-block).

C-c C-e

Close the innermost LaTeX block not yet closed (latex-close-block).

In LaTeX input, \begin and \end tags are used to group blocks of text. To insert a block, type C-c C-o (latex-insert-block). This prompts for a block type, and inserts the appropriate matching \begin and \end tags, leaving a blank line between the two and moving point there. When entering the block type argument to C-c C-o, you can use the usual completion commands (Completion). The default completion list contains the standard LaTeX block types. If you want additional block types for completion, customize the list variable latex-block-names. In LaTeX input, \begin and \end tags must balance. You can use C-c C-e (latex-close-block) to insert an \end tag which matches the last unmatched \begin. It also indents the \end to match the corresponding \begin, and inserts a newline after the \end tag if point is at the beginning of a line. The minor mode latex-electric-env-pair-mode automatically inserts an \end or \begin tag for you when you type the corresponding one.