Actually, this is pretty simple.

First step :
In your main plugin file, where you put the description, you add the text domain :

/*
* Plugin Name: My plugin
* Author: You
* Text Domain: plugin-domain
*/

use the php function __() to put your strings in it, and create .pot file to make your translated strings.

Example :

$lang = “english”;
sprintf __(“my %s string”, $lang, ‘plugin-domain’);

This is a simple example, you can find more in the codex and with google 🙂

If you need a hand don’t hesitate 😉

EDIT : have a look here, it will be a start : http://codex.wordpress.org/Function_Reference/_2