If you are referencing a conference paper which has been printed in a book as part of a collection of papers you can reference it like a chapter in a book.
The details below are for conference papers presented at a conference which have never been formally published.
1st citation
First name Surname, “Title of conference paper,” (paper presented at Name of Conference, Place of Conference, Month Year), page number(s).
Gary Templin, “Creation stories of the Middle East,” (paper presented at Northwestern Annual Conference, Evanston, IL, April 26 2000), 17.
Subsequent citations
Surname, “Title of conference paper,” page number (s).
Templin, “Creation stories of the Middle East,” 21.
Surname, First name. “Title of conference paper.” Paper presented at Name of Conference, Place of Conference, Month Year.
Templin, Gary. “Creation stories of the Middle East.” Paper presented at Northwestern Annual Conference, Evanston, IL, April 26 2000.