This feature is only available in the desktop editor.
Click anywhere on your image > select annotation options
In the screenshot below, you can see the mouse is clicking on the image.
After you click on the image, a selection of annotations appear at the top of the desktop editor. Select the annotation you would like to use.
Click and drag your mouse on the image
To draw an annotation, click and drag your mouse on the image. As you hold down the mouse, and move the mouse across the image, you will draw an annotation.
The sequence annotation and the text annotation do not require you to drag your mouse to draw them--those annotations will automatically appear when you click on the image (and after you select the annotation).