To do this, first open Preview (simply click on a picture file). Then right click on the Toolbar > Customize Toolbar > Drag and Drop the Annotate Button to the toolbar and click Done.
Then, when you open a picture file, you'll be able to use the Annotate button to draw arrows, squares, circles, and much more! You can even add notes to a picture, in case it's a picture of your cat that you'll be e-mailing to icanhascheezeburger!
Got a question, tip or comment? Send them to firstname.lastname@example.org and we'll try to answer it in a blog post!