Starting/Restarting/Stopping your server
To start/restart/stop your server first click on your minecraft server in the sidebar. This will take you to the Console page of the instance you selected. You can find a guide on finding your instance here https://www.creeperhost.net/wiki/books/minecraft-java-edition/page/finding-your-instances
In the top right of the Console page there are 3 buttons in green, orange and red. The green button will start the instance if it is stopped, the orange is to restart the instance, and the red will stop the instance.
If the instance is unable to start for some reason, you will get a notification at the bottom of the screen with a message saying it was unable to start the server.