hidden code

I found a thread here that talks about adding hidden code. Where do I go to add this code?

Thanks. I'm new at this.

there's no way to make this automatic for all users?

Thanks.

There is an option under others in BBcode instead of typing it.

You can also set permission for links and images => https://help.forumotion.com/frequently-asked-questions-f5/set-permissions-on-the-images-and-links-in-the-posts-t57364.htm but nothing for words.