Once loaded, the editor registers a global object called FCKeditorAPI. This object offers the entry point to interact with any editor instance placed in a page (you can have more than one).
NOTE The FCKeditorAPI object will not be available during the page load. You need to wait for the editor to be loaded to use it. If you need to interact with the editor right after is has been loaded, use the "FCKeditor_OnComplete" function (see "Events").