If you are citing a study with three, four, or five authors write the authors names separated by commas and use the word and to signal the last author.
Kisangau, Lyaruu, Hosea, and Joseph (2007) found
For subsequent citations write the first author’s name followed by et al.
Kisangau et al. (2007) found
Omitting the Year
Omit the year from subsequent citations after the first narrative citation within a paragraph.
Kisangau, Lyaruu, Hosea, and Joseph (2007) found that this was true. Kisangau et al. also found…
Include the year in subsequent citations if the first citation within a paragraph is in parentheses.
Studies show that this is true (Kisangau, Lyaruu, Hosea, & Joseph, 2007). Kisangau et al. (2007) found…
(American Psychological Association, 2010, p. 175)