Some information is found in API.txt (DRUPAL-6--1) in the Features folder.
Making your module support Exportables
The section "Integrating your module with the Features API" in the api above outlines the basics. The handbook page on exportable configuration explains how to make the data stored in your db tables exportable via either CTools or Entity API.
If you're working with data that involves user roles, see the handbook page on exportables and user role IDs in features
To make your variables exportable, without writing any code, you can use strongarm http://drupal.org/project/strongarm. The directions on the front page of strongarm under the heading "Updating your features from Strongarm 1.x to 2.x" cover this.
To see how other modules implement features and use strongarm, do a search for:
features[variable]in .info files
'export' =>in .install files.
'EntityAPIControllerExportable' =>in .module files.
A simple test module that supported features for the examples module would be a great place to start learning features