There isn't a glossary creation tool in InDesign. A glossary has a list of words followed by their definitions, but doesn't need to refer to the page number.
However, finding all the terms required for the glossary is something else. If the words used for the glossary have used a special Character Style (and not just bolded/italicised as an override of the format) then a script called "indexfromcharacterstyle" by Martin Fischer can do this. It creates an index based on the words which have a specific character style applied to them. A link to the script is here: http://indesign.hilfdirselbst.ch/text/indexeintrage-auf-der-basis-von-zeichenformaten.html but it's in german so may have to use Google Translate.
If the words used for the glossary have been coloured using a different colour, then the script called "index_from_colour" by Thomas Silkjær could help. Works in a similar way to martin's script but looks for text colour rather than character style. It can be found here: http://mac.softpedia.com/get/Graphics/Index-From-Colour.shtml
In either case, it will make the list of words within the book that need definitions. From here it is a case of adding the definitions.
Dear Colly, thanks for your answer,
I've download the charactar script, but your last sentence;
From here it is a case of adding the definitions.
seems to be a problem for me..
Sorry, still working on figuring it out, but if someone can help giving a suggestion on how to add a definition to the index list, i would appriciate it very much.