WYSIWYG stands for What-you-see-is-what-you-get. It's a handy editor that enables you more features and moreover lets you paste articles without adding any colours or functions. So in short, it will allow you to post the exact layout of the articles (colours, bolds etc added) without you manually adding it.

In order to use this editor, go to your User control panel (at the top titled User CP)

Select Edit Options and and scroll down to the bottom part where it says

Message Editor Interface

Change from the Standard Editor to Enhanced Interface - Full WYSIWYG Editing and voila, you're done.

Remember that you can always change it if the editor doesn't suite you. Just re-iterate the above steps again.