Website content, like any other kind of content, is subject to copyright laws. That means you can't take it without asking.
That's why you have to be careful when you write your own website content. Make it original.
If you're not a writer, then you might get the impression that anything that appears online is free for the taking. That's not the case. All website content is subject to copyright and fair use laws.
That's not to say that you can't ever use other people's content on your blog or website. There is public information online that is re-usable. Generally speaking, however, if you don't see an explicit statement of permission on a website that outlines under what conditions you can use content, then you should assume that you can't use it at all without permission.
When writing your own website content, make sure it is original, unique, and speaks to your target audience.