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.

The quick answer is that you always should tell the reader where the information is from when paraphrasing what someone has written or said. However, there is no black and white answer that goes for every occasion and all subjects. 

• Common knowledge that won't be refuted usually doesn't need a reference. This can for example be dates for well-known events or other commonly known facts.
• Common knowledge within the field that the text covers usually doesn't need a reference since it stands no reason for the readers who work within the same field. You yourself have to make the decision about whether a reference is needed or not.  
• Your point of reference is always the reader and what he or she can be expected to have knowledge about already, or need a reference to. 

You should always have the reader as your frame of reference. It should be easy for the reader to understand what part of your text is connected to the different sources and what possibly is your own comments or conclusions. 

Strive to make the text as readable as pooible and thus inserting the reference smoothly. The reader should no have to stop the reading in order to read out your reference. Also, there is no need to repeat the reference unnecessarily as long as it is clear that it still is the same source. If you have a longer paragraph that comes from the same source, it can be clarifying if you make the reader aware of the fact that it is still the same source that is being referenced. This is also a good way to, if needed, clarify that it not your own opinion that is presented. You do this by using reporting verbs together with the author:

Example:

• Greene emphasizes… Greene implies… Greene describes…

 There are a lot of different reporting verbs to choose from. Vary the verbs and choose according to what is fitting in the context.

Exemple: 

• demonstrate, write, explain, present, point out, consider, show, illustrate, agree, discuss, confirm, claim, conclude...

If the paraphrase continues into a new paragraph, reintroduce the citation. 

Read more about referencing on APA Style: Appropriate Level of Citation

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.

Example:

Parenthetical:

The marine animals that inhabit tide pools enjoy swimming (Doe, 2018).

Narrative:

Doe (2018) studied the swimming habits of marine animals i tide pools. 

Recommendations:

Although there are no rules for when to use narrative or parenthetical citation, there are some tips and guidelines you can follow:

• Do not use narrative and parenthetical citation in the same sentence. It can get messy.
• Use narrative citation when you want to highlight the author for some reason, for example when you refer to two authors who agree with each other or have different opinions.
• Switch between narrative and parenthetical citation in a text to vary the text and make it more readable.

Read more:

Should I Use Narrative or Parenthetical Citation? Walden University Writing Center

Parenthetical versus Narrative In-Text Citations. APA Style

Repeat the reference when switching between different sources so that it is clear what source is connected to the given information. Read your sentences carefully to ensure you have cited the sources appropriately and that it is clear to the reader. 

You should, as far as possible, avoid citing something that is being quoted or paraphrased in a secondary source, and instead try to find the original source. If you can't get hold of the primary source and you still think it is important and relevant to refer to the secondary source, you can use the following suggestion that goes for APA Style.  

In APA you refer to the original author(s) in the running text but cite the secondary source, i.e. the source that you have read and taken the quotation from. Include the publication date of the original source, if it is known to you. In the reference list, you write the reference to the secondary source, which is the one that you have read. In the following examples, it would accordingly be Englund and Smith that is found in the reference list. 

• Cats have been popular pets for ages (Chambers, 1876, as cited in Englund et al., 2019)
• Wilson (as cited in Smith, 2015) states that this is ...

Read more about this on APA Style: Secondary Sources

If you refer to several works at the same time, they are stated in alphabetical order by author and then in chronological order. Semicolons are used between each reference. The order is then the same as in the reference list and it is easy for the reader to find them. 

• Man's eternal dream of conquering space is manifested in many different ways (Eco, 2005; Johansson, 2006; Thulin, 2000, 2004)
• Meurling talks about gender roles and ideals of beauty (1999, 2003)

Read more on APA-Style: Citing multiple works

Titles of works are usually not mentioned in the in-text citation. If you want to draw special attention to a certain work for some other reason, the title is written in italics. Italics is used for books, reports, web pages and other stand-alone works. For works that are part of a greater whole (e.g. journal articles or edited book chapters), do not italicize the title or use quotation marks. 

• Example: Harry Potter and the Philosopher's Stone is the first part of the Harry Potter series. 

Ibid. is not used in APA style. You should always use author and year in the in-text citations, also when the same citation recurs. 

From American Psychological Association. (2020) Publication manual of the American Psychological Association (7th ed.). https://doi.org/10.1037/0000165-000 (p. 266)

Copyright 2020, American Psychological Association

Read more on APA Style: Parenthetical Versus Narrative In-Text Citations