Plagiarism is every use of text from other sources that is not properly marked (quotation mark, reference). How to use sources properly? See examples:
Author J. Kowalski in book Forget-me-nots published by PWN in 2004 wrote:
Forget-me-not are blue.
Option 1. Quotation
Use quotations only in definitions. It can look like this:
According to J. Kowalski "forget-me-nots are blue" (Kowalski 2004, p. 32).
or shorter (to avoid mentioning name twice):
According to J. Kowalski "forget-me-nots are blue" (2004, s. 32).
Quotation marks and reference are required.
Additionally in References section add:
==References== * Kowalski J. (2004), Forget-me-nots, PWN, Warsaw.
Option 2. Paraphrase
Paraphrase is more comfortable and should be used in most cases. It can look like this:
According to J. Kowalski forget-me-nots during growth become blue (Kowalski 2004, s. 32).
Shorter version of reference is also possible.
In paraphrase quotation mark is not necessary, as we don't quote, but paraphrase. But the reference is still required, as the entry in References section
Examples of errors (plagiarism):
Forget-me-nots are blue -- copied text forget-me-nots during growth become blue -- paraphrase without reference According to J. Kowalski "forget-me-nots are blue" -- citation without reference According to J. Kowalski forget-me-nots are blue (Kowalski 2004, s. 32). -- no quotation mark in citation
Check your text and add any lacking quotation marks and references.