If you are referencing a specific page or pages, include the page numbers after the year, separated by a comma. For example: (Jackson, 2015, p. 123).
If there are two authors, include both last names, separated by "and". For example: (Jackson and Smith, 2015).
If there are more than two authors, include the first author's last name followed by "et al." and the year of publication. For example: (Jackson et al., 2015).
In your reference list, list the textbook in alphabetical order by the author's last name, and then by year of publication. Here is an example of a reference list entry for a textbook:
Jackson, J., & Smith, M. (2015). Introduction to Psychology (4th ed.). New York: Oxford University Press.