You know what parenthesis are, right? I'll put my home state (South Dakota) in parenthesis.

Parenthetical is an adjective referring to the stuff that is is parenthesis.

So the first part of that big fancy word means the information that is inside parenthesis.

What's that?

You know a document could be a piece of paper, a Google Document, a WORD document. But what if the doctor told you to document (a verb) every time you had a headache. What would that mean? The doctor is wanting you to write it down--to document it. Make a list. Make a chart. Take a picture of the day on the calendar. Whatever. But somehow document it. Provide proof.

So, documentation, as in parenthetical documentation, means to write down where the information came from.

Thus, parenthetical documentation.

Here's another term: Annotated Bibliography

That's a combination of a works cited page and a short summary of what the source it about.

You probably won't have to do that until your a jr. or a senior.

For psychology classes & other related subjects, you might use APA. This makes you write the source with the publishing date. Why? Well, think about medical research? Wouldn't you want the most accurate and up to date research?

There might be other reasons your instructor tells you to use APA, but that's the one that'll make sense to you now.