Embed part of a website into my website

Use the page attributes, see if there is an option to select No Footer/No header:
https://docs.wpbeaverbuilder.com/assets/images/remove-the-header-and-footer-d17b8bca-665ff07822ba8a0e08ea96c830fe7615.jpg

If not, you can create your own:
https://www.webpreparations.com/create-wordpress-page-without-header-footer-sidebar/

Sorry I did not explain myself clearly. I I would like to embed only part of someone elses webpage into my website. I need to embed the content of a page but not the menu, header and footer.

Not possible.

Can I embed the entire page useing IFRAME and hide the header and footer with CSS?

afaik, you can’t do this unless the iframe is coming from the same domain.

You could look at setting a CORS like this:
https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

Alternatiely, you could ask the owner of the other site to implement some js and css like this – which tells the browser to remove the header and footer if the page is loaded into an iframe:
https://gist.github.com/danieliser/59c01eae386c58c0592655d28a3be165