How do I include a book, magazine article, report, etc. in the reference list if I retrieved it online, from a database for example?

In the reference list, the publication is included as an online source, as there may be a difference between the online and printed versions. Some databases, such as Nexis Uni, do not always mention page numbers.
For accurate referencing, look for the appropriate category in one of the libguides on APA Style.