MyBB Community Forums

I realize about the thread here: http://community.mybb.com/thread-23946.html but it doesn't explain how to do it though.

I only have 3 questions about this.

1. What do I type into the cookie prefix? Can I type anything in there such as maybe "VisualizeEdits" as my cookie prefix or does it have to be short like "VE" or something? http://gyazo.com/5941d8f37fcfa064f07e2c48c7bfd52e

2. When I change the prefix, does it automatically fix it in the settings of my php file? (config.php)

As of last, I have multiple MyBB forums under the domain of VisualizeEdits and I'm hoping that this will fix the login issue that I'm having.

3. If I add a cookie prefix, do I have to add one for all my other forums? (Not the same name though)

cookie prefix can be anything (however try to use short words - may be < 11 characters)
changing the cookie prefix at the admin panel automatically stores in to settings.php file
different forums you have in the sub-domains should have different cookie prefixes

follow the suggestion given by frostschutz at your earlier topic