When your reader says something like: I think you may have copied some of the sentences from wikipedia or another webpage
On one hand:
Your reader may be alerting you to unintentional plagiarism, so this is a comment you should take seriously.
If you are using ideas or words that are even partially from a web page, you need to use documentation to identify your source. See documentation and plagiarism for more information and resources.
Use this webpage from the University of Wisconsin writing center to see how to use your sources without plagiarizing.
On the other hand:
If you have not used sources, and your reader says something like this, it may be more about the way that you’ve written your paper.
Your reader may be sensing that you are just summarizing information, but not providing analysis or an argument. If this sounds like the case, start by thinking about whether you’ve included enough analysis.