Plagius detects whether part of the document was copied from a web page. In this regard, the level of accuracy achieved by the program is high, but due to its operation mode and dependence on search engine results, there is a margin of error.
The best way to find plagiarism is to manually review the analyzed document and check for sections of text with many highlighted phrases (blue to red colors). In these cases, it is very likely that the paragraph has been copied.
Another way to find plagiarism is to check the addresses with the highest number of occurrences. There is a good chance that these addresses are the source of part of the analyzed document.
Regardless, the program suggests possible occurrences of plagiarism. Only a manual review of the results can determine whether it is actually plagiarism or not. For more information on this topic, see valuable tips for identifying plagiarism with Plagius.