A citation gives credit to the source where you found the information you use to support your argument or analysis. That way, people can check the information you used to double-check your resources or to use for their own research.
Citations are composed of these parts of a resource: Author, Title, Publication Information, and Date. The elements of a citation can vary from format to format and how the resource was accessed.
In your paper, you will add a brief citation that will lead to a page of the resources you used at the end of your paper where the full citation goes into more detail. That way, your paper flows and can be easily verified.
Nowadays, most library databases have a "cite" function that will generate a full citation in the style you need. You can use that as a starting point and re-format or correct it as you need.
Other resources don't generate a citation, but they have the information for you to create one, you simply need to look through the resource.
An in-text citation is a part of the full citation that is at the end of your work that guides the reader to the specific source you used. Where the full citation is of the whole resource, an in-text citation will be part of the full citation (either author or title) and maybe a specific section such as specific pages.
There are two ways to have an in-text citation in a paper: parenthetical and narrative.
A parenthetical is the citation at the end of the sentence in parenthesis ().
A narrative citation has the information written into the sentence.
Sometimes you might do a combination of the two—it depends on your writing style, the resource, and your professor.