Use View and Markup
You can use the View and Markup tool to add markups to items, allowing you to annotate items without altering the item itself.
All markup entities are saved in a markup file, which is associated and overlaid on the image. There can be more than one author per markup file. A new layer is automatically created for each new markup file author (determined by the login user name), allowing them to see other author's markups but not edit them.
If you'd rather use your preferred editing program on your computer to add markup to items in document containers, you can use the Desktop App to make items available offline.
To start learning about View and Markup, take this tutorial.