To put a term in the index, use a command like one of the following:

\index{add an index entry}
\index{index!making an entry}
\index{Gauss C@Gauss, C.}

The first simply creates an index entry for "add an index entry''; the second creates a subentry "making an entry'' under the main entry for "index''; see the index to this manual. The third example makes an entry for "Gauss, C.'' but alphebetizes it as if it were "Gauss C''.

When you index a term, you should follow it immediately by the index macro, with no intervening spaces, to make sure that the index command ends up on the same page as the term being indexed. Use:

reciprocity\index{reciprocity}

not:

reciprocity \index{reciprocity}