To distinguish between morphological forms during the search process, you should create file 'lang.cns' and then save it in the directory, where index files will be stored. This file is not included into the distribution kit because of its large size - 16 Mb.
If 'lang.cns' file is not found, the search and indexing process will be performed without taking morphology into account.
A special utility has been developed in the system allowing building 'lang.cns' from ispell dictionaries. You can find necessary dictionaries at http://fmg-www.cs.ucla.edu/geoff/ispell-dictionaries.html. Ispell dictionary consists of two files - a list of words (lang.dict) and a set of word formation rules (lang.aff). If these files have different names in downloaded archives; then they should be renamed to 'lang.dict' and 'lang.aff'.
Note: If you have already built the index taking into consideration morphology, you should take into consideration morphology while entering a search request and use the same dictionary.