To change the author, title and subtitle, click on the second icon in the top left (make sure you're on the new Touch UI.. editor.html editor version) and page properties will come up. Scroll down to edit the title and subtitle. Then at the top, click 'general' to change author and category. To save changed, click the checkbox.
Add some post content here. Click once to get started. You can align left and right and if you click on the 'square' icon to the left of the 'X' icon, you can edit in full screen mode.
Also, you can remove the image above by double clicking and dragging on a new image. Alternatively you can click on the image once and hit the trash can icon to remove it. You can drag as many images as you'd like.