Global Actions are available on all pages. The following screenshot shows Global Actions:
You can also create a new custom global action by using a custom Lightning Component. The navigation path from set up manager page is Setup | Global Actions.
The following screenshot shows how you can add a custom Global Action using a Lightning Component:
For custom Global Actions to appear, the Salesforce administrator needs to add the action to Publisher Layouts. The navigation path for Publisher Layouts is Setup | Global Actions | Publisher Layouts.