Q. How to cite sources in the research paper in the paragraph in APA style?

The instructions for in text citations in APA varies based on whether you are using a direct quote, paraphrasing or how long it is. I've included the two most common scenarios. You can see more here. 

Paraphrase
When you paraphrase (put into your own words) ideas from another author's work you still need to cite it. All that is required is a reference to the author and year of publication. It is possible that your instructor might also require page number, so be sure to check.

Example: 

Though most teens belong to at least one social site, there is very little peer reviewed research on the topic (Thompson, 2012). 

Exact quotations With Less Than 40 Words Including Author’s Name
When the quotation is less than 40 words, you have to use quotation marks. In the example below, the reference is placed immediately before the final punctuation of the sentence.  A list of all sources cited in the paper must be included at the end of the paper.

1. Separate the elements (author’s name, publication year and page number) with commas.
2. When the author's name does not appear within the quote, place the author's name, the date, and the page number in parentheses at the end of the quotation.

Example:

She stated, “The ‘placebo effect’ . . . disappeared when behaviors were studied in this manner” (Miele, 1993, p. 276), but she did not clarify which behaviors were studied.