Place it in plugins/autosave directory where CKEditor is installed and don't forget to add 'autosave' to config.extraPlugins
CKEDITOR.config.autosave_delay - delay in seconds before request is sent (located in config.js)
CKEDITOR.config.autosave_extra_post_data - object with extra data to be passed to the server with POST request
input[id=AUTO_SAVE_URL] - input (usually hidden) with save url (located on the page)
Setup config variables and make your server to send back on POST request {status: ok|error, (optional message: text)}
Boris Shemigon