If you just want to insert a tab character in the buffer, you can type C-q TAB.
To move over the indentation on a line, type Meta-m
back-to-indentation). This command, given anywhere on a line,
positions point at the first non-blank character on the line.
To insert an indented line before the current line, type C-a C-o TAB. To make an indented line after the current line, use C-e LFD.
split-line) moves the text from point to the end of
the line vertically down, so that the current line becomes two lines.
C-M-o first moves point forward over any spaces and tabs. Then it
inserts after point a newline and enough indentation to reach the same
column point is on. Point remains before the inserted newline; in this
regard, C-M-o resembles C-o.
To join two lines cleanly, use the Meta-^
delete-indentation) command to delete the indentation at the
front of the current line, and the line boundary as well. Empty spaces
are replaced by a single space, or by no space if at the beginning of a
line, before a close parenthesis, or after an open parenthesis.
To delete just the indentation of a line, go to the beginning of the
line and use Meta-\ (
deletes all spaces and tabs around the cursor.
There are also commands for changing the indentation of several lines at
once. Control-Meta-\ (
indent-region) gives each line which
begins in the region the “usual” indentation by invoking TAB at the
beginning of the line. A numeric argument specifies the column to indent
to. Each line is shifted left or right so that its first non-blank
character appears in that column. C-x TAB
indent-rigidly) moves all the lines in the region right by its
argument (left, for negative arguments). The whole group of lines moves
rigidly sideways, which is how the command gets its name.
M-x indent-relative indents at point based on the previous line
(actually, the last non-empty line.) It inserts whitespace at point, moving
point, until it is underneath an indentation point in the previous line.
An indentation point is the end of a sequence of whitespace or the end of
the line. If point is farther right than any indentation point in the
previous line, the whitespace before point is deleted and the first
indentation point then applicable is used. If no indentation point is
applicable even then,
tab-to-tab-stop is run (see next section).
indent-relative is the definition of TAB in Indented Text
mode. See Text.