Commenting is easy in Mockingbird! First, click the little comment icon in the toolbar.
You'll get a little yellow comment icon as your cursor. You can then click wherever you want to add the annotation. This can be on top of an element or anywhere on the page you choose.
If you are annotating an element, you'll see a yellow outline when you hover over the element.
Once you click wherever you want the comment to be, you'll see a text box.
Type some text and hit enter. Now your comment has been saved.
If you're just annotating a spot on the page that isn't a particular element, you won't see any outlines when you hover, but you can simply click anywhere on the page.