In CSE style, the abbreviation et al. should appear in a reference-list entry for a source with (four/ten/eleven) or more authors.

In the Council of Science Editors (CSE) citation style, the abbreviation "et al." should appear in a reference-list entry for a source with four or more authors. Here are the steps to do it:

1. Write the surname and initials of the first author followed by a comma.
2. After the first author's name, write "et al."
3. Follow this with the publication year in parentheses.
4. Then, write the title of the work.
5. Finally, provide the source details such as the journal name, volume, issue, and page numbers for a journal article, or the city of publication and publisher for a book.

For example, if you are citing a book with four authors, the citation would look like this:

Smith, J., et al. (2005). Title of the book. City of publication: Publisher.