The editor graph works and look pretty much like the Animator graph, this is the editor for the State Machines they are composed of nodes with Actions, Triggers and Transitions where you can add Conditions.
To create a Behavior Graph asset right click on your Project Panel and select
Create → Game Creator → State Machine. You can name it however you want as well as place it anywhere.
In order to run a State Machine you have to use a State Machine Controller component. You can add it manually to a Game Object or simply drag and drop a State Machine asset in an object this will auto-create a State Machine Controller and assign the State Machine reference.
To bring up the StateMachine Graph window simply go to the top toolbar and select
Window → State Machine. Alternatively, when you double click on a State Machine asset it will automatically open the window.
When playing Unity you can preview where the State Machine is currently running.
Once you right click somewhere in the Graph it will show a different context menu depending on what you have selected.
One neat feature of the State Machine is that you can easily export them to re-use them on other projects.