An editor is available online to edit your books. A new build will be started each time you save a file. Refer to the section "Draft Workflow" if you want to write a draft of the book without building it.
The editor is accessible on each of your books. From the book's dashboard, click on the "edit" icon, it will open a new tab with the editor.
The editor is compatible with all modern web browsers: Google Chrome, Safari, Firefox and Internet Explore; check that you're using the latest version of your web browser.