A more extensive guide to APA from Purdue's Online Writing Lab (OWL). You may need to click through the tabs on the left to find the information you need.
Publication Manual of the American Psychological Association
The APA 7th Edition is the complete manual for citing material and formatting your paper according to APA guidelines. The library has multiple copies on the bookshelf behind the Reference Desk. Spiral bound copies can be purchased online for around $40.
Despite the unappealing interface, the APA Style Blog is created by the folks at APA and the search box usually turns up answers to the even the most difficult APA style questions.
Publication Manual of the American Psychological Association