Choose the diagram you want to publish and click "share". In the dropdown menu you can select where you want the diagram to be posted.
If you want the diagram to appear on ProcessOn only, click "Publish on ProcessOn" and fill in the required details.
You can publish you diagrams on other websites as well to reach a greater audience. To do so, click "Publish on other websites". Copy the link provided to post the diagram in other social networks.