MyBB Community Forums

I'm using icyboards.net and I want to know how to add plugins like shoutbox ?
 Can Someone help me ?

IcyBoards is not providing shoutbox plugin. instead you can use IRC [see this]

Shoutboxes use a ridiculous amount of resources, even when properly tuned, when hundreds of users are logged in at once. It pretty much needs it's entire own server. IRC is much more light weight and pretty much has no resource footprint.