How to make pages 404

Hey all, I was wondering if anyone has a tutorial, or knows more detailed way on how to make pages 404.

So why do I need to know this?

Because, I bought an aged domain, and I want to do 301 redirects, I know of one WordPress plugin redirection that helps me with it.

But it's got some pages that I don't want, So, I need to do 404, but I can't find a proper tutorial on how to accomplish this very thing.

Can anyone help me with it, please? I'd greatly appreciate your time

Hi!
Do you just need to create empty 404 pages? Which will be more familiar to people?

You can install safe redirect manager by 10up from WordPress plugin directory. Once installed then you can redirect the pages to your default 404 page.