You reference according to APA style by citing the author/authors and year of publication, i.e. the information that you then put in first and second place in your reference list. This makes it easy for the readers to know where in the alphabetical reference list they should look for the complete reference to a specific source.
For the in-text citation, cite only surname(s) and year, even if the reference list entry contains a more specific date. For references with no date, use "n.d." (no date).
See the table in Basic Styles to view the two different ways to reference with either the whole source in parentheses or the author outside the parentheses.
See the table Basic Styles to view the two different ways to cite with either the whole source within parentheses (parenthetic citing) or the author outside the parentheses (narrative citing). You choose yourself what fits better in your text and you can use both alternatives in the same text. To use both ways is also a way to vary your text.
The marine animals that inhabit tide pools enjoy swimming (Doe, 2018).
Doe (2018) studied the swimming habits of marine animals i tide pools.
Although there are no rules for when to use narrative or parenthetical citation, there are some tips and guidelines you can follow: