First, make sure you have a template that provides Bootstrap (such as dokubootstrapsimplified or dokutwitterbootstrap)! These provide necessary CSS, and without them, the alert boxes won't show up.

Search and install the plugin using the Extension Manager. Refer to Plugins on how to install plugins manually.

Simply use this syntax to add differently colored alert boxes:

<alert info>Here is an informational message.</alert>
<alert warning>Here is a warning message.</alert>
<alert danger>Something dangerous is happening!</alert>
<alert success>Something good is happening!</alert>

Good luck!

You can make this plugin compatible with Igor changing following lines in syntax.php:

function handle($match, $state, $pos, &$handler){

to

function handle($match, $state, $pos, Doku_Handler $handler){

and

function render($mode, &$renderer, $data) {

to

function render($mode, Doku_Renderer $renderer, $data) {