There are a couple of ways to draft and preview your content with Capitan
Status > Draft Mode (committed drafts)
Capitan has a "Status" called "Draft Mode" which allows you to create commited draft content, saved to the database. When the content is in "Draft Mode" it is published to the website but is only visible to authenticated Capitan Administrators. So you can be logged in to Capitan and developing your draft and seeing how this looks in the website while making your changes.
When you're ready for the content to be visible to the general public simply change the "Status" to "On".
Generate a Preview (uncommitted drafts)
If you're making changes to content but you aren't ready to save these to the database you can click "Generate a Preview" which will build a preview using the content found in the editor at that time.