The definitive source for guidelines using APA style is the Publication Manual of the American Psychological Association, frequently referred to as the "APA Manual." Most recently in its 7th edition, the manual will contain information for formatting papers, in-text citation examples, bibliography help, and sample papers, including information specific to student papers.
Publication Manual of the American Psychological Association by 
Most word processors include an APA Template where elements like the running head, title page, sections, and references are already set up. You can begin a paper this way by opening Word, click "New", and searching for "APA" in the templates search box. Keep in mind, however, these templates will likely reflect APA 6th edition style (for now). Different word processors may have slight variations in their templates. It is YOUR responsibility to ensure their accuracy.
Here's a quick list of some of the major changes from the 6th edition to the 7th edition of the APA Manual:
Samples for professional papers, student papers, and annotated bibliographies are now included
Running head and author note is no longer included in student papers
One space (not two) should be used after a period
Publisher location no longer required for book citations
With three or more authors, abbreviate "et al." the first time you present the work in in-text citations, as opposed to writing all authors the first time and using "et al." subsequent times.
For a general mention of a website with no indication of specific page, no reference list or in-text citation is needed.
In your reference list, write out up to 20 author names as opposed to 7 authors maximum. For 21 authors or more, use ellipses.
Present both DOIs and URLS as hyperlinks, and do not insert "Retrieved from" before a hyperlink.
More citation examples are included for social media, apps, media, and other non-traditional sources.
For more help, see these links below:
DOI stands for Digital Object Identifier
The DOI is a a web address linked to the publisher information of an article or book chapter. This enables all readers to access basic information about your article, regardless of their affiliation with a library or other institution. Most DOI links do not resolve to full-text, however, so it shouldn't be used for bookmarking for full-text access. DOI links or numbers can be searched in DOI.org to reveal identifying elements of an article like title, authors, and the abstract.
Most recent online articles will include the DOI as part of the first page of the PDF version, usually in the header or footer, along with the source of the publication:
You can also find it in many database results by clicking on the title of an article, instead of the PDF directly. This will reveal an organized list of identifying features about the article, including title, abstract, authors, and publication information. The article DOI is often included in this information.
If you can't find a DOI in either of these places, you can look up a DOI using the CrossRef website to search for the article title in the Search Metadata box:
In some cases, there simply isn't a DOI for an article. If you found the article from a library database, end the reference after the page range and do not add a URL. If you found the article on an online journal website that is accessible to all readers (not from a library database), use the URL to the article at the end of your citation.
In the latest edition of APA, the DOI should be formatted as a URL at the very end of your citation, like this:
https://doi.org/10.1037/ppm0000185
Do not end with a period, and use the automatic formatting in Word to make it a hyperlink.
Many articles may list the DOI as a string of numbers or a phrase:
Be aware, you will need to reformat as a URL to place into your citation, regardless of how the journal formats the DOI.
