Workflow files are created and run in Automator, while Applications can be used without opening it.
Every app that can be controlled by Automator is listed in this Library pane.
After choosing an app, the second column will show the actions you can ask that app to perform. You drag them into the pane on the right in a specific order, such as New Mail Message and then Send Outgoing Messages.
For apps that do not include actions, you can record your keypresses using the controls in the topright corner (which adds a Watch Me Do action), and export them as a workflow or app to be activated at any time.