In order to index the current selection or the word at the cursor
press C-c /
(reftex-index-selection-or-word). This causes the
selection or word ‘word’ to
be replaced with ‘\index{word}word’. The macro which is
used (\index by default) can be configured with the
variable reftex-index-default-macro. When the
command is called with a prefix argument (C-u C-c /),
you get a chance to edit the generated index entry. Use this to
change the case of the word or to make the entry a subentry, for
example by entering ‘main!sub!word’. When called
with two raw C-u prefixes (C-u C-u C-c /),
you will be asked for the index macro as well. When there is
nothing selected and no word at point, this command will just
call reftex-index, described below.
In order to create a general index entry, press C-c
< (reftex-index). RefTeX will prompt
for one of the available index macros and for its arguments.
Completion will be available for the index entry and, if
applicable, the index tag. The index tag is a string identifying
one of multiple indices. With the multind and index packages, this tag is the first
argument to the redefined \index macro.