When you press <F9> in insert mode after \cite{pre, Latex-Suite will present a list of valid bibliographic keys starting with "pre" and ask you to choose from one of them. ("pre" can be left empty in which case all valid bibliographic keys will be listed). The window setup is as described in section Latex-Suite completion example.
<F9> will also work in a similar way after any command which contains the word cite in it. For example, pressing <F9> will also work with \citenum etc.
The following logic is applied to find out which bibliographic entries are included in the completion.
Firstly, if the present file has a master-file defined for it, then Latex-Suite will perform the following steps on that file instead of on the current file.
First, the file is scanned for a \bibliography command. To explain better, assume that a command
\bibliography{file1,file2}
is found in the present file. For each bibliography file, say file1, Latex-Suite first tries to see if a .bib file, file1.bib can be found. If so, it will scan it for bib-keys of the form @BOOK{ etc., and add these searches to the completion list. If a .bib file cannot be found, then it will try to see if file1.bbl can be found. If so, Latex-Suite will search it for bib-keys of the form \bibitem and add these to the completion list.
You can set the location where Latex-Suite will search for .bib and .bbl files using the |Tex_BIBINPUTS| variable.
If a \bibliography command is not found, then Latex-Suite tries to scan the present file for a \begin{thebibliography} environment. If found, Latex-Suite searches the present file for bib-keys of the form \bibitem.
Finally, it will try to see if this file includes other files via the \input command. For each such file found, Latex-Suite will repeat the previous two steps stopping at the first file which has either a \bibliography command or a thebibliography environment.
Often times, the editing cycle proceeds by first laying out a comprehensive bibliography and then completing all the \cite commands in one session. In such situations, it is inefficient to scan the whole list of bibliography files for bib-keys each time. Latex-Suite provides a way to cache the results of the cite completion search using the Tex_RememberCiteSearch variable. If set, Latex-Suite will perform the search only the first time <F9> is used. Next time on, it will reuse the search results. If you wish to redo the search results, issue the command
TClearCiteHist
This will redo the completion list next time you use <F9>.