In general, you simply use the copy and paste function of your operating system. If you're not familiar with how to do that, check out the help system on your computer.
For most systems, you can access cut/copy/paste by highlighting any text block and pressing the right mouse button. Shortcut keys are usually available suce as Ctrl+c for copy and Ctrl+v for paste.
When copying text from another website or a news organization, please be aware of their copyright requirements. Almost all of them will require an attribution of some sort when you copy material from them.
[Edit a few minutes later]
I see from your other post concerning quotes that you know how to copy/paste. Therefore, I have no idea what the problem is. Please explain in more detail what doesn't seem to be working to get text from another thread or site into a reply box.