For in-text citations in APA format, if there are two authors, it should look like this: (Smith & Jones, 2006)
If there are three to five authors, format it like this: (Smith, Jones, Lewis, Brown, & Washington, 2003) - note the commas and ampersand placement.
If there are more than five authors, format it with the first author's last name, followed by "et al." (Jones et al., 1993) - note that there is no punctuation after et, but both a comma and period after al.
You can use the same setup for the signal phrase, exchanging the ampersand for the word and:
Smith and Jones (2006) argue, "..."
As indicated by Jones et al. (1993), "..."
