How to add red arrow to picture

To expand on ~Bee's answer, I use Preview too. Here is when the arrow function is located:

Note there is a keyboard shortcut shown to access the arrow function without working through the menus.

There are many tools that can do this. The one I use on a Mac at the moment is Skitch.

tt2

SnagIt does that as well.

Theres a great little app that comes with your Mac called " Preview."

Open it, and then look at "tools."

I use Preview as well.