1) Log into your ACP.
2) Make sure you have your shoutbox code copied, and ready to be pasted soon.
3) Click on the 'Posting' tab.
4) Click on 'Add a new BBCode'.
5) In the 'BBCode Usage' box, enter [shoutbox][/shoutbox].
6) In the 'HTML Replacement' box, paste your shoutbox code into the box.
7) Click 'Submit'.
Your BBCode production is now complete, now you just need to insert the BBCode into a forum description.
8) Click on the 'Forums' tab.
9) Find an input box which has the button next to it called 'Create new forum'.
10) Enter your forum name in the 'Create new forum' box.
11) Click the 'Create new forum' box.
You will now be taken to the page where you setup the forum you just made.
12) In the 'Description:' box, type [shoutbox][/shoutbox]
13) Change any other settings you want on the page (not necessary).
14) Click 'Submit'.
You will now be taken to another page where you setup the forum permissions. Make surr you set the group 'Registered Users' can view it, and lock it to registered users.
You now have a fully functional shoutbox working on your phpBB3 forum!
-SawanM.