In-text citation format
APA uses author–date parenthetical citations. Place them at the end of the sentence before the period, or integrate the author into the sentence and put only the year (and page) in parentheses.
Paraphrase
Stewart's framework reorganizes how memory is conceptualized in cognitive science (Stewart, 2019).
Direct quote with page number
Memory, Stewart writes, is "less a storehouse than a workshop" (2019, p. 47). Page numbers are required for direct quotes and recommended for paraphrases of a specific passage.
Three or more authors
(Brennan et al., 2018) - use et al. from the very first citation when there are three or more authors. APA 6 spelled out all authors on the first appearance; APA 7 dropped that rule.
Organization as author
First citation: (World Health Organization [WHO], 2019). Subsequent citations: (WHO, 2019). Only abbreviate if the organization has a recognizable acronym you will reuse; otherwise spell it out every time.
No date
(Stewart, n.d.) - the abbreviation goes in the year slot.